I've often wondered about this myself as .357 is the one caliber I can't seem to find any consensus on what is considered the best or one of the best. All I can say is it seems pretty much anything .357 is really freakin' good, but from the countless videos of ballistic gel testing and articles I've read, this is what I've learned:
Anything Winchester .357 is questionable, to me at least. Their white box .357 is the same bullet loaded into their white box .38 Special +P load. Well, that bullet is meant to work at .38+P velocities, not .357 velocity. The bullet fragments into pieces when it hit water while the .38 worked perfectly. The PDX1 .357 expands fine, but the velocity and energy is low for .357; I'm talking a muzzle energy of just under 500 ft-lbs out of a 6 or 8 inch barrel. If you want power in your .357, I think you should look elsewhere.
Almost anything Federal is boss. Most of I've read has only good things to say about Federal .357 ammo. Good energy, good expansion, good penetration, good bullet weight retention. If you can get Federal .357 hollow point ammo for a good price, you will have some good ammo.
Hornady is good too and I think their Critical Defense .357 is absolutely the best for .357 revolvers with 3" barrels or less. I don't know much about their American Gunner .357 load, I don't know it's performence in gel, but I know it's pretty hot load and can be got for $17/25 rd box and often for less than that. If the bullet expands well and retains it's weight, I think it will go down as the best quality, economically priced .357 defense ammo.
Remington is well known, but for both good and bad reasons. I personally have decided to not touch their guns or ammo ever again because of quality and performence issues going back to their acquisition by Freedom Group. Their .357 ammo seems to have jacket separation issues, but their .38 ammo is some of the best in the world. Bottom line on Remington is I think there's better out there for both .357 and .38 ammo.
Speer is good.
Buffalo Bore... well if you gotta kill something, there's nothing wrong with overkilling it! This is the HOTTEST .357 magnum ammunition available in both 125 gr and 158 gr and is loaded with Gold Dot bullets. One shot of Buffalo Bore center mass is going to kill anything in the Western Hemisphere you shoot it at except maybe bears and moose.
This is what I know about the big names in ammunition. The Magtech's, PMC, Aguila, Armscor, etc. are cheaper for a reason. They might work, but they'll never be as good as what I mentioned above.
The energy produced by the .357 will usually make up for any shortcoming in bullet choice for SD. Hunting is a different story. I'm not talking about short barrel loads that throw a light 135gr bullet @990 fps. 
