I've never been able to decide between Shapeshifting kind of deal or Telekinesis.
With shapeshifting, even if you have to adhere to conservation of mass, you still have alot of options. Feel like you have too much fat? turn that fat into muscle! If you figure out how, why not give your body the ability to photosynthesize? Need a disguise? A dime a dozen! Old feeble body? Fix those rusty joints! Just got your leg blown to bits during a fight with a supervilian? ('cause lets face it, you're using these powers to fight supervilians) Don't worry, just grow it back! You must be this tall to ride this ride? You ARE this tall to ride this ride! This role requires someone who looks older/younger/prettier/grittier/etc? Oh you know some guy, he'll be here in a couple of minutes!
If you aren't stuck looking human, you could get real crazy. Four arms for extra points of manipulation. Grow a tentacle with an optic nerve in it to see around corners and in places you would never be able to see. Leaf the Dream and spend a day as a tree, because you know you always wanted to be a tree!
The telekinesis however has so much versatility.
Near infinite points of manipulation allow for incredibly fine actions. You could open locks without tools so long as you know how the lock works. You could actually get the dregs of the peanut butter out of the jar. You could reach anything, no matter how inaccessible it is, so long as you can see it (or even if all you need to know is where it is, or that it exists). Press every button on a keyboard without missing if you practice enough. In fights this gives allows you to use anything that's hard, heavy, and/or sharp as a weapon, no matter how unwieldy or numerous. Hell, you don't even need to use a weapon, why not just crush their organs?
It can also mimic just about any other ability. Flight? Levitate yourself. Fireballs? Throw flaming oil at them. Mind Control? Can't do that, but how about the next best thing: Body Control! Your not even cheating when you try to do the various bending abilities, and you get to do all of them!
To sum it up: Practical immortality, with none of the drawbacks (aside from emotional, but if things start looking bleak, just stop regenerating) versus Basically every power that affects the physical world rolled into one convenient package.
In the end, I still can't decide.
EDIT: added thoughts and fixed derps.
As a shapeshifter you could create your own clothing (such as cotton, wool, or leather) just by growing the bits into an already woven/tanned outfit (a bit Skuicky [http://tvtropes.org/pmwiki/pmwiki.php/Main/Squick] but what are you gonna do?)
Also, so long as there is some kind of organic conduit for a power (like if psionic powers come from a structure in the brain) you could grow those organs with shapeshifting, so maybe shapeshifting is the most powerful. And who's to say you can't asexually reproduce by making a perfect clone of yourself and splitting it off?
