get gh3. it's one of those games you never get tired of because of it's great online multiplayer. mp3 looks pretty...but loads of people just don't care for it's actual gameplay. not to mention it's lack of split-screen. and smg is a great game and all...but...uh...well it's amazing.
so i guess that narrows it down to getting gh3 or getting smg and saving 50$ it all comes down to what type of game you're in to.