Depends what you plan on doing with your Tanker (solo, team, both ... TFs, regular missions, AEs, PvP, PvE, etc ...)
In general, you'll want most of the shield powers. The only ones that are ever really skipped are grant cover and, sometimes, one with the shield. Grant cover doesn't give *you* any defense, and its short range means it doesn't usually give *anyone else* any defense either. It does give you defense debuff and recharge debuff resistance, but you have to balance that with the cost of a power and the end. One with the shield is a relatively weaker godmode - it compensates for this by having a much milder crash and through being up more often, but some don't care for it. Everything else in shield is essential - even phalanx fighting, which many don't realize has a base defense boost even if nobody's next to you.
From stone, in my opinion the must-haves are the mallets, seismic smash, and fault. Between the mallets, stone fists (which is actually a decent attack) and seismic smash, you have a ridiculously damaging single target chain, and fault is just absurdly good AoE mitigation between the stun and knockdown. If you have the extra slots, buildup, taunt, and tremor are also worthy powers, but it depends on your preferences. I would take them, but that's me.
@MuonNeutrino
Student, Gamer, Altaholic, and future Astronomer.
This is what it means to be a tank!
Stone Melee skippable powers:
Stone Fist (but you're stuck with it so... 
)
Build Up (IMO highly skippable for any tanker)
Hurl Boulder (aptly named IMO)
If your build is tight, Stone Mallet is your next most skippable.
The Stone Melee "must have" are:
Heavy Mallet (I snag it at 4 generally)
Taunt (in my opinion a valuable tool for any tanker)
Fault (Only Stamina takes precedence, get this at 22 and slot it up. 2 accuracy SO's at a minimum as it has lower base accuracy)
Tremor
Seismic Smash
Shield really doesn't have any truly skippable powers; the closest candidate is Grant Cover... but it's holding a good chunk of your debuff resistance hostage. If you're teaming with a group of shield characters GC is very valuable... I leveled my BS/Shield scrapper with a SG team of all shield scrappers and we all had soft capped def as soon as we got GC.
I would snag Deflection at level 1, then True Grit, Active Def and AAO as soon as they come up. Battle Agility I'd want to try to squeeze in fairly early; Phalanx I'd grab in the 20's as even solo it's worth 5% def to you. Shield Charge is a simply awesome AOE attack and aggro getter that should come ASAP.
One with the Shield I've found useful but not mandatory on my scrapper; for a tanker I'd try to squeeze it in sometime.
I realize I'm listing more "get early" powers than you have room for in the early levels so you'll need to prioritize based on your own needs and playstyle. You could put True Grit off a bit and take Battle Agility in it's place but you likely would have problems running both your defense toggles prior to Stamina, that's why I've suggested TG instead at that point.
Active Defense as your mez protection I place as a "get the instant it's available" power. Against all odds is your aggro aura as well as a damage boost; if you're tanking you'll want it early.
Remember to slot end reduction in your attacks, Stone Melee is fairly high end useage and you'll save more end with one SO in Heavy Mallet than you would with an endred in EACH of your toggles... so keep that in mind.
Overall, once you get the end problems under control in the '20's the Shield/Stone combo should be very effective. Just realize going in that it WILL be end heavy... particularly in the low levels.
COH has just been murdered by NCSoft. http://www.change.org/petitions/ncso...city-of-heroes
So i just got back to the game a week ago after a year+ break and have never played either power sets, what powers should i avoid or flat skip and what should i def be taking, ill post my build in the morning when i can get mids to work for me, but just wondering what powers i should be taking outta shields mainly cuz they all seem good to me.