What a tanker has extra on defence, most of the sets* lack on offence. There are some set-combo's that can do nice damage, but they are not build to do so.
Solo wise they have some issues early game due either low attack or they cannot keep up their shields due low regen.
Most important, pick the set _you_ like, not wich one is 'considered best'. Each set is based on a playstyle, alot also on the IO's (invention origens). You like a superman style? Go Willpower or Invul along with superstrength. Rather being a 'thor' style? Sadly tankers have no electric armor (brute does), but u can have a nice slapping hammer!
First, enjoy and learn the game. Once u know alot, you can make a final choice what you like best. Maybe a scrapper is better afterwards, or even a controller or blaster.
set: The selection of your primairy and secondairy powers.
50)Sinergy X/(50)Mika.
(50)MaceX/(50)Encore
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Welcome to the game/forums!
What sets are you interested in?
I would start every AT as a beginner and alternate them until say level 20 before picking a main. You can get an idea on how others play their archetypes from different perspectives and come up with an idea on how all yours would theoretically work together. You would also of not gone too far without the opportunity of seeing what other opportunities could be had if you went with different powerset.
He will honor his words; he will definitely carry out his actions. What he promises he will fulfill. He does not care about his bodily self, putting his life and death aside to come forward for another's troubled besiegement. He does not boast about his ability, or shamelessly extol his own virtues. - Sima Qian.
I agree with Shannon,
But i'll give a very brief run so you know roughly where to start.
Scrappers and tanks are melee toons (close combat) tankers can take alotta damage (high hitpiints like over 2300) but dont give out much, where as scrappers do high damage but cant take as much due to low hit points (around 1600 i think)
Controllers, can slow, stun, hold, sleep with there primary, an there secondry is team buffs, to give more damage/regen/debuffs etc etc.
Blasters are ranged damage dealers but cant take much damage
And lastly defenders, who do weak primary ranged damage an have high buff powers healing, speed boosts etc etc like a controllers secondry but stronger.
Send me a message on here or ingame @Effy for any help 
@Effy
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Effy Unleashed DP/EN Blaster 1st 50 @ Union
Hmm some tanker tips....
Okay, here we go. First of all i don't play with Tankers but tried a couple in the past and have one leveling at the moment.
Your biggest turn down probably will be endurance (that blue bar under your green hit point one which represents your energy for using your armor/shields or attacks), you can over come it by sloting 2 endurance reduction enhancements on your toggle armor/shield powers. Also you can think of slotting 1 endurance reduction enhancements into your attacks.
If you won't go for Willpower primary set, better arrange your powers according to get Stamina as soon as possible(level 20). As Stamina is the last power of Fitness pool you need to pick up two other powers before it to make it available at level 20. You can start taking power pools from level 6.
Get your status protection power as soon as it is available if you want to enjoy your tank. Status protection, protects you from many nasty effects like sleep, hold, disorient or immobilize. Other than Fire or Dark it also gives you Knockback protection.
That's the most important things came to my mind for now. If you need any help in game you can contact me from my global chat handle; @Knightly. For sending a private tell type /t @Knightly, <your message> on your chat box.
Have fun and i hope you enjoy your stay in Paragon City.
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Rather being a 'thor' style? Sadly tankers have no electric armor (brute does), but u can have a nice slapping hammer!
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War Mace (customised to battle hammer) + Willpower + Mu mastery Brute 
But yeah, Heroside you cant really do this. I agree with others though, play what you feel is fun - its important to have fun as your first toon.
Some sets are geared towards playstyles though. Like to not get get? Ice is for you. Like to take a beating and for it to not hurt? Invuln. Like to be durable? Willpower. The others i would describe as hybrids with tricks to make up for thie rlack of specialisation (i'll leave stone out since its an anomaly imho).
Hope this helps
I've been playing tankers for 2-3 years now, heres a few tips that might help.
Earlier levels you WILL take lots of damage and most likely die a lot, up until level 22 at least when you can slot better enhancements (single origin enhancements- a lot more effective than the ones you can get before that level).
It is frustrating not being able to effectively do your job and tank, but stick it out until this level and you will then be able to stand in the middle of a mob and laugh
Endurence is a real pain for tankers, for a newcomer i would recommend willpower just because the endurence recovery power helps lots, also dont forget the pool powers on fitness from level 6 onwards so you can get stamina at level 20. This is a staple power of almost every build.
Taunt is almost always needed especially for someone new, there is possible builds where you dont need it but you will always perform better with it plus it doesnt cost endurence or need accuracy so why not?
The biggest issue I see with new tankers nowadays is they act like there afraid of the mob, they run in and get the agro then run back into the rest of the team and hide behind them, most of the time getting everyone including themselves killed.
The best way to avoid this is what tankers call herding. You basically run in first, taunt or attack a group of enemies while the rest of your team waits, then hide behind something so the mob has to run up to you in a group, usually not far from the rest of the team. This is often a skill which determines a good tank and a bad tank.
If you want to be a good tank, remember that tanks take damage mainly, not deal it. I've seen a lot of wannabe tanks (or scrankers - scrapper tankers as there known) take a lot of damage powers before there armor powers, this often leads to the team going splat as soon as they enter a mission. Good tankers tend to only have one or two attack powers before level 20 because of all the armor powers they take and pool powers.
For a beginner to tanking I'd definately recommend staying away from ice and shield until you get a little more experience within the field. In my opinion they are very hard to start tanking with because they are defence based rather than resists which brings me onto my next point nicely...
The difference between defence and resist is that you take less damage per hit, defence is the chance you will actually be hit. Effective tankers have a mix of these but also 1% defence is supposed to be equal to 2% resists, but anything over 45% defence doesnt improve your stats because the enemy will always have a 5% chance to hit you (cap limit) where as resists are at 90% and if you can reach that you will be able to withstand most attacks from that type of damage with ease.
Tanking is one of those things that is harder than it first looks, but i strongly recommend you tell people in your team that you are new so they can decide whether to get another tank as well, which would be helpful for you because then you can watch the other one and learn from them.
If you would like a crash course in tanking and play on union, feel free to send me a message @Predatory I'm always willing to help those who need it
That last post was longer than i thought 
Anyway since I know its going to get asked (it usually does by new players) there is no real 'best' tank set, everyone of them is good in there own way it just depends how you play it. Quick breakdown though:
Dark: High overall resists, very reliant on heal but needs constant watching of hp and endurence to play effectively. Low defence, no knockback resist. Very endurence heavy needs good slotting especially on heal.
Fire: More offencive version of dark armor, 'swaps' having lower resists for more damage output and another build up power, these are the hardest hitting tankers (some people will argue shield but after playing both, its fire ) also has a heal
Shield: highest tanker defence style set, relys on not being hit and is pretty hard to tank with until you get to 50. Shield charge is a great power to help get agro with as well and does a lot of damage. Tends to be endurence heavy as do all defence sets. Has no heal.
Ice: the only tank ive not actually played to 50, its another defence style tank, from what ive seen they dont tend to do well in pve and are nearly always the first tank to fall pre-50. Still people say they are awesome in pvp. Has a heal.
Invulnerability: My personal favorite, a mix between high resists and average defence. Can reach 90% smash and lethal resists easily, heal takes a long time to recharge but has +hp on it as well. One of the easier sets to tank with for a new player.
Willpower: Not too different to invul, has lower resists but also a defence, stamina style power and lots of regen. The easiest tanker to use for a new player.
Stone: The best tank at taking hits effectively with granite on, however the problem is you are slowed down heavily which means often you need to switch between your armors to tank well and get agro. Your armor toggles don't work together and you need to switch between. Has a heal.
Think thats em all
Hi everybody, as you can tell i'm brand new :P im just wondering if anyone has got any really big helping tips for me on starting a tanker, i will be even soloing or working with a friend and i believe that tanker will be a very fun way to go about it
Also could people refrain from using in game abbreviations as i don't really know what they mean lol, unless you explain it then that's all good