You said it all...
Spines: Great AoE damage plus 2 good ST powers (Impale and Ripper)
Katana: Great ST damage plus defence bonus. (It blooms later than Spines tho).
The combo DP+IH+Quills+SpinesBurst is just uber. You'll be nuking mob after mob quicker than any other Scrapper. Plus, Spines might be better for PvP (at least for Sirens) while Katana blooms later.
Anyway, both combos are great fun. Spines will kill mobs faster, Katana is better for bosses/ebs/avs since its ST damage is awesome.
@False Fiction - Virtue / Defiant
Current projects - [Glaciologist - Ill/Cold Troller] [Cloudshaper - Storm/Dark Def] [Harald Wartooth - Elec/Psi Domi]
Spines also has a number of ranged attacks. Shouldn't forget that, very useful in a Scrapper.
Theoretically a kat/regen Scrapper has one of the highest survival probabilities in the game. (Broadsword is about the same, but BS's forte is DPS and lots of Parrying cuts your DPS.)
Point to note: While Scrappers are generally boss-killer types, /regen Scrappers suffer from one big weakness, Alpha Strikes. They soak up damage great, until you do a lot rapidly and then they keel over like they're made of tissue paper. Lots of DEF and RES insps are a good idea.
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I would pick Katana/Regen.
I'm basing this on having a 50 Kat/Reg and a 38 Spines/Reg and I'll give my reasons why.
My level of enjoyment was a lot higher playing the Kat/reg as that set enables you to become a high threat killer, such as Bosses, AV's - as mentioned above.
This specialisation of role appealed to me - particularly in the 40+ levels.
Spines/Reg is a great AoE minion killer but I found the High, quick Damage of the Katana more appealing.
One last thing is that the Kat set has 2 of the best high end ST attacks in Soaring Dragon and Golden Dragonfly. These round the set of very nicely and add to the 'fun' factor of the Kat set.
The very last thing .. 
RW is correct Regen's Achilles Heel is being overloaded with damage all at once, so you can't heal quick enough. I would highly recommend taking Tough before you get to level 35 and if you can't then certainly by level 40.
Proud member of FOXBASE ALPHA and coalition associates.
Hero 50's - 25
Villain 50's - 1
Magic , cheers guys. I think i am gonna keep both active but favour the kat/regen build as it's looking like the most fun build , it's even stoping me logging on as my lvl 41 ill/rad troller ( & i rally love that toon ).
Cheers again.
hermight
One thing that hasn't been mentioned is the secondary effect of Spines. Pretty much all the powers have DoT toxic damage and -spd and -recharge. The -recharge is often overlooked as an aid to survivability. It's of the order of around -10%, with Throw Spines being twice as good IIRC, so you can easily get a 30-40% debuff on most of the spawn from quills, Spine Burst and Throw Spines. Obviously that isn't as good as 30-40 defence from Katana, but it is free.
I found spines a very fun set but a little underwhelming at low levels, mainly because of some of the animations being pretty long. However once you have got Ripper slotted, the set becomes good. Throw Spines is then really good once you work out how to use it best.
@Unthing ... Mostly on Union.
Agreed the -speed and -recharge are very handy in the Spines set.
I'm certainly not knocking Spines, as I intend to take my current Spines/Reg to 50.
It's purely a personal opinion to go for Katana - for the reason given.
My only observation on Spines is that I wish I had taken it with /Inv instead of Regen. I've seen a couple of Spines/Inv Scrappers lately that were very impressive indeed and were able to take a lot of heavy damage.
Proud member of FOXBASE ALPHA and coalition associates.
Hero 50's - 25
Villain 50's - 1
Really good advice , cheers guys. I have just given both toons an hours play each & am gonna go with katana for the pve side of the game, but spines seems to be so much more geared towards pvp ( which is a part of the game i have never really got into ). Not sure wether it's the regen aspect of the builds but atm it's faultless ( hopefully not famous last words ).
Tks again
BTW , is DA as good as it looks to be ( defence wise ) ?
hermight
According to sherky silver, Ripper has the same damage as Golden Dragonfly. But, katana looks so much cooler even if ripper is a double backflip
According to No-Future, Ripper does less damage than GD, by quite a bit. I'm happy trusting No-Future, I think it's been updated in the last century.
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Damn you sherky silver =P
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Really good advice , cheers guys. I have just given both toons an hours play each & am gonna go with katana for the pve side of the game, but spines seems to be so much more geared towards pvp ( which is a part of the game i have never really got into ). Not sure wether it's the regen aspect of the builds but atm it's faultless ( hopefully not famous last words ).
Tks again
BTW , is DA as good as it looks to be ( defence wise ) ?
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Spines has some nice PvP benefits, Impale being ranged and having a immob and -fly is the main one. However it is really more of a crowd control set rather than a single target set. It still does the single target thing pretty well, but not as well as say katana.
By crowd control I don't mean immob/holds and stuff, that's too subtle for a scrapper. I mean just good honest AoE damage.
DA is a good set but it is endurance heavy. It has the best self heal in the game ( IMO ), combined with all round resistance ( including Psi ), 2 crowd control power ( fear and stun auras ), a self stealth and a damage aura. It's main flaw is the lack of knockback protection.
@Unthing ... Mostly on Union.
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DA is a good set but it is endurance heavy.
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DA is better than Regen for sheer volume survival. It does lack KB resistance, but then it has Psi resistance.
And yes, it has a horrible endurance drain problem. 
Disclaimer: The above may be humerous, or at least may be an attempt at humour. Try reading it that way.
Posts are OOC unless noted to be IC, or in an IC thread.
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According to sherky silver, Ripper has the same damage as Golden Dragonfly. But, katana looks so much cooler even if ripper is a double backflip
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1. Never trust SherkSilver - it's an excellent planner but the numbers can't really be 100% trusted
2. The number SherkSilver gives for Ripper is if you get the maximum amount of DoT, which is pretty rare.
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BTW , is DA as good as it looks to be ( defence wise ) ?
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Not sure if you're talking about Dark Armour or Divine Avalanche but as this is a Katana Scrapper I'll assume the latter - yes it is very good. As a Regen you probably won't need to use it constantly but it will be useful against large groups and tough mobs. I prefer to think of it as an attack with a handy defence buff rather than a defence buff which also does some damage, so I slot it 2xAcc, 3xDamage, 1xDefBuff to keep my damage per second as high as possible.
Hadn't actually thought he might mean Divine Avalanch... 
If you slot it 1xACC, 2xRecRed, 3xDefBuff, the damage is terrible, but you get about 23% Def buff. Add Hasten and you should be able to have it overlapped twice (so, three buffs) about 75% of the time, assuming you always hit.
A kat/regen scrapper has a phenomenal ability to "absorb damage" if slotted up this way. It either misses you, or it gets soaked up in your regen. A kat/dark armour scrapper is theoretically better, but tends to run out of endurance before the fight is over. 
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I slot my Divine Avalanche 2 Acc, 2 Defbuff, 2 Damage, which I find to be an excellent overall effect. I used to have it slotted for recharge and 3 Defbuff but the difference in defensive power is (in 99% of practical situations) negligible, whereas the 2 x Damage improves my DPS noticeably, if not to a world-beating level. If I really need more defense, I pop purples or hit Hasten.
Katana/Regen is an extremely tough combination if you take DA and all the options. I don't have MoG yet (and I will), but even without it my defensive options are layers of DA, Reconstruction, Dull Pain, Instant Healing and Hasten. Of all the characters I have, it's the one that possibly benefits most from Hasten - with Hasten on, I can pretty much chain the 3 heaviest attacks with DA between each one, and Reconstruction comes back very quickly. It's a great character to play.
SPines for both pve and pvp
unless u wanna solo
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I don't have MoG yet (and I will), but even without it
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It's actually not worth using DA with MoG. MoG can already pretty much cap out defense on most enemies, and adding in the defensive bonus from DA doesn't really help. (For the pedants: Yes, I know defense doesn't have a cap. I mean that MoG will floor the ToHit on the majority of opponents.) since they changed the way Def affected your accuracy, DA+MoG actually became less likely to keep you alive since anything above a minion now has more chance of hitting you than it did prior to the changes.
Just FYI. A kat/regen Scrapper is still a pretty tough beastie. 
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Just a bit of advice needed on these builds.
I have both of these builds at lvl 18 and am unsure which to take further.
Kat seems to have a lot more damage potential + with DA has a nice def bonus.
Spines just seems to be aoe & not as powerful.
Any advice before i pick 1 to hammer to 50 ?
hermight - Lvl 50 fire / fire tank