It sounds like the pre-draft market doesn't support a 1st rounder for Brandon Marshall. I really don't know what it would take (w/o paying the full 1st & 3rd price) to get Jackson. Let's say for argument's sake that, to get either one of them, it would take a 2010 2nd + a 2011 4th that could escalate to a 2nd based upon performance and behavior. The market for troubled WR seems to be at a fairly low point (Holmes).
I personally think that Marshall is the bigger off-field risk & on-field reward. I would prefer either of them for a 2nd+ than Dez Bryant at #12 because (a) it allows us to get a premium defensive player and fill two holes and (b) I like a proven WR rather than taking a flyer on a college WR.
I do not believe we should stand pat with our WR corps with the number of options apparently available to us. It will kill me if NE or NYJ walk away with Marshall (or potentially Jackson) for a 2nd+ and we end up with the same WR corps as we have and 1st & 2nd round defensive picks who may or may not be impactful NFL players.