moosecats,
as you know, in NE with Tom Brady, EVERYONE gets the ball there... including some defensive players (i.e. Mark Vrabel)... so going with gabriel he would give you some great weeks, and some goose eggs...
with Drew Brees in NO, his main targets in SD were Keenan McCardell and his big target Antonio Gates... i feel that Horn is going to take the McCardell role, and Colston is going to be Brees' Antonio Gates, Brees has been quoted to 'be in love' with Colston's big play ability on third downs making him a reliable option for him consistently. At 6'4", whats not to love?
If both were on the free agent wire, and you needed help at WR and have a spot, I would definitely pick him up... i already have!