It would depend on how the game actually plays, but the first icon looks like more of an arcade/action game icon to me whereas the simple style of the second one I often associate with puzzles. If I was scrolling through the app store the second icon wouldn't necessarily stick out to me as a boxing game.
I prefer the top one. It's got character. Although the nipples are quite spaced out! LOL. The second one doesn't appeal much. It looks less professional and wastes half the space with background.
I agree with AnonNimus. The first one reads immediately as "boxing". People might not get the second one right away. If that's important. Both nice designs, though!
I like the top one a lot better -- it's more distinctive -- although the character seems a bit weirdly "stretched out" in the right 30% of the image, to the right of the boxing glove. Good luck with your game!
I prefer the bottom one but that's after I've seen the top one and knowing it's a game about boxing (right?) I suggest putting the boxers in the ring (bottom icon) . Or making the top icon a little smaller and moving the hand a little. It looks kinda weird.
