wonderful....yet another thread devolves into a geno debate... :hijacked:
as to the actually questioned asked in the OP, i don't really see the need to bring in a veteran WR. but of the choices given, i'd go with shorts. he is 27 (turns 28 in late december), whereas johnson will be 29 by the time the season starts and jennings turns 32 in september.
jennings days of being a deep threat seem to be long over. instead of averaging something like 16-17 ypr as he did in his prime, he's now a 10-12 ypr guy. johnson has seen a steady decline in production, although perhaps under gailey he can reverse that trend. so i'd have some interest in him, but only on a short-term and relatively cheap deal.
i can't say i know too much about shorts since he's been stuck in the wasteland that is jacksonville his entire career and has played with dreadful QBs. to me, he seems to have more upside potential than the other two, who imo, are clearly on the downswing of their respective careers.