(Stats courtesy of http://www.footballoutsiders.com/stats/wr
Wallace: 72 catches on 114 targets, 1193 yards, 410 DYAR, 32.2% DVOA
Marshall: 81 catches on 142 targets, 1227 yards, 251 DYAR, 9.8% DVOA
Jackson: 60 catches on 115 targets, 1106 yards, 268 DYAR, 15.5% DVOA
Wallace: 60 catches on 98 targets, 1257 yards, 457 DYAR, 48.8% DVOA
Marshall: 86 catches on 114 targets, 1014 yards, 127 DYAR, -1.8% DVOA
(Jackson only played 5 games due to suspension/contract holdout)
Wallace: 39 catches on 72 targets, 756 yards, 232 DYAR, 29.6% DVOA
Marshall: 101 catches on 155 targets, 1127 yards, 179 DYAR, 2.3% DVOA
Jackson: 68 catches on 109 targets, 1170 yards, 448 DYAR, 38.7% DVOA
I imagine in their book FO will have detailed YAC numbers showing where these guys catch their passes and what they do with them.
Since Wallace became a starting WR he's put comparable numbers on fewer targets than either of them. While Wallace catches his share of bubble screens most of his routes are vertical routes down the field with lower chances of success. Marshall puts up his numbers because he is a compiler. There's no way to compare receivers against one another 100%, but Wallace has better numbers. He also has substantially less baggage than both of them and is younger. Anyone who wants one of the other two receivers is acting like the kid who wants someone else's toy even though his toy is shinier and nicer.