keep SMG, it'll have so much replay value no one can possibly pay enough to take it away from you.
Sell ME on e-bay or amazon and you'll get more money. Shovel someones driveway (assuming there is snow where you live) or mow someones yard for some spare cash, and go buy Zack & Wiki.
I'm not much of a person for selling games, especially not a game of the quality of SMG. I haven't played ME, but I still probably wouldn't sell it myself, but since you said you have to trade in 2 games, i'll go with trade in one and work for the other. 








