Well what i would do is look at he reviews for each one, and see which one has the best. But also ask your friends and people who have 360's and see what they say.
But if you really can not decide after that, just assign each one a number, and a roll a pair of dice.
MERCENARIES!DUDE IF YOU HAVE XBOX LIVE,YOU CAN PLAY CO-OP ONLINE WITH 1 OF YOUR FRIENDS!He can join in on your game or drop out anytime he likes and he wont interupt your gameplay.Merenaries WIF is probably the best on your list!
Ive played the 1st mercenaries game and it was awsome so the 2nd should be great as well. Ive tried soulcalerber 4 and from what ive experienced its a erally good game as well(plus u can play as jedi, great for those star wars fans like me)
I'd say mercenaries, because soul caliber is about the nice chick and fighting but that's like all. Both should be good but i think there's more freedom in merc 2 and also more thigns to do.
Get SC4, or if ure patient get fallout 3. It should be what type of games you prefer. Fallout 3 seems to be more hyped up though. In the end im getting all of them nearly =-0