I prefer Harvin, he had a great second half of last season after a slow start. He can also see some rushing attempts this year. I do not think Wallace will hold out during the season, but I would not take the risk. I think Maclin is in for a solid year. He will be the red-zone target over DJax, and will see plenty of targets. I rank them... Harvin Maclin Wallace
I'd keep an eye on Maclin (not sure how long you have), make sure that hammy doesn't continue to bother him. If it does, then I'd rank him last out of all three, thats not an injury that just goes away. See Miles Austin.
Harvin will probably be the main focal point of this offense, if he sees an increase in playing time from last year. I think he can be a top 10 WR, if he gets the time on the field.
With Wallace, I'd be weary of guys holding out all training camp. I don't care where you are, and who you supposedly trained with, nothing replaces wearing pads and getting hit during practices. I would expect a slow start for him whenever he does show up.
I like Harvin a lot this year and Maclin is poised for a big come back year. He added 8 lbs of muscle and is totally healthy going into camp and pre season. I think its between them two. Mike Wallace is explosive obviously but the holdout sets him back a bit. Plus he never has been big on receptions. Flip a coin between Harvin and Maclin. Its splitting hairs IMO