With Michaels, Marte doesn't have to be traded, so it's Michaels+Marte vs. Crisp. This is, of course, assuming that Michaels can be had for a RP+ deal. Look at how Michaels stacks up against Crisp defensively in CF.
Player, GP, F%, RF, ZR, Rate, Rate2
Michaels, 138, .983, 2.67, .855, 107, 108
Crisp, 188, .986, 2.42, .866, 93, 94
Most of the traditional stats (Fielding %, Range Factor, Zone Rating) are very similar, which makes it weird for their Rate stats to be so far apart. Since I don't know the equation to calculate RAA (Runs above average, which is used to determine Rate), I can't tell you what Michaels has done to get such better numbers than Crisp. Let's just throw those out and call them defensively equivalent.
On the offensive side, Michaels has a better OPS, OBP, and EqA, but Crisp hits for more power. So, if you think the Sox need another power threat (I don't), then Crisp is who you want. But, if you want someone to get on for the sluggers they already have (I do), then Michaels is the answer.
Obviously, Crisp has much more upside, and despite the statistcal oddity, I suspect he's a better fielder. But his potential, extra power, and better glove aren't enough to warrant giving up Marte IMO. If a deal for Mota+(non-big-5 prospect) can net them Michaels, then that is a better deal than the one for Crisp+(filler).
EDIT: I had the Rate stats backwards, Micheals' numbers are better.