From watching AOT we've seen just how destructive titans and Titan shifters can be. But we've also seen how tough their bodies can be.
As the have much too many flaws to really fit in marvel here are the powers they should keep/have.
- Peak human strength, speed, reflexes, and agility.
- moderate superhuman regeneration ( strong enough to regenerate limbs and organs but not the head)
- long lived 500-2k years (taking their regeneration in to account it would only make sense)
- limited electrokinesis (only because they can summon powerful lightning strikes over themselves. That can also be used in destructive ways)
-limited shapeshifting ( in the Titan form they will have self sustenance and whatever extra powers of the Titan form)
- hardening
- steam generation (stream powerful enough to burn and give blisters.)