I agree with most of the other guys concerning "most powerful" status. It's really not meaningful until you define the target.
I suppose it would be proper to say that the one that put out the most foot pounds of energy at any given distance from the barrel would be the most powerful.
The trick is in deciding what you want that energy to do.
Is it penetration for penetration's sake you are after as in shooting deep into the heart area of a cape buffalo?
Is it energy that is used for breaking the shoulder bone on an animal to stop it's charge?
Is it energy that has been put into expansion within a given depth of penetration (say, 12" or less) that you want as in self defense/carry ammo?
Depending on what you want to accomplish the greatest foot pounds of energy at the the barrel may not mean much to you.
You may, for instance, have the greatest foot pounds of energy with a very fast stepping hollow point and it may do no more that make a grizzly mad.
On the other hand you may have a great ammount of energy on paper and end up putting a very narrow 357 caliber hole in one side and out the other on a bad guy.
Both would be the wrong choice for "the most powerful" round regardless of the paper energy readings.
If it is self defense ammo we are talking about, the name of the game is achieving maximum expansion possible for the caliber by the use of a good hollow point that is consistent and holds together - while limiting the energy to a number that will not shoot through most bad guys but will penetrate adequately.
If absolute expansion is achieved, it is the rare case where over penetration is something that needs to be worried about - at least with 357 caliber bullet weights and handgun velocities. On the other hand it is often hard to make the heavy weight bullets expand in a human target at handgun velocities and over penetration can become a real problem.
Bottome line, to me, is that a fast stepping 125 gr. hollow point is the "most powerful" on humans and the fastest stepping heavy solid is the most powerful on big game.
My 2 cents worth!