My thoughts as a Raiders homer:
First, I am not sure Porter goes. I hope he does, I think shipping his Ashley Lelie routine out of town would put some bite behind Art Shell's very tough bark. However, the Raiders tend to be player friendly, it is rare for a player to be considered a lost cause (Philip Buchanon notwithstanding). Also, the Raiders don't have to do a dang thing with him. There's no rush. His contract isn't expiring, he has zero leverage. And it's not like the Raiders to give players away in deals. As bad as they've been in recent years, it's not because of bads trading. There's a good chance they could let him rot on the roster till he wises up.
Having said that, I think there's a good chance he's gone, or as good as gone (by being benched, whatever). If so:
Going by what I've seen, Curry, when healthy, has been the more reliable receiver. He worked mostly in the slot, and was often looked for on third down. And still has deep speed. Gabriel worked mostly outside the hashes, and was a favorite target of Collins on deep routes. Now, maybe Gabriel has the ability to be a possession guy as well, perhaps it was just the situation, and the previous staff's scheme. Can't say for sure. But the general consensus in Raider Nation was that Curry, despite a new position, was more polished as a receiver.
But I'm not expecting anything from Curry this year. Three Achilles injuries? He seems to be a great guy, I root for him, but I am not optimistic. Maybe I should be, he has said he is 100%, and has been working out full speed in camp, although not with the team (is that a contradiction?). The point I'm trying to get at is his injury is not considered a current situation.
If I had to make a prediction, assuming all are healthy:
Moss gets his numbers, and Curry and Gabe have good weeks, then quiet weeks. If all are healthy, I see their numbers being close. Maybe Curry with more catches, and Gabe with more big plays.
So, considering the health issue, I'd go with Gabe, especially in leagues that reward big plays.
Super sleeper: If Curry goes down, and Porter is gone, a nice guy to have on deep leagues for an occasional start could be Alvis Whitted. He's a smart vet, who is very fast, knows the system, and might be the best possession guy after Porter on the team. Every year we Raider fans think he's getting cut, and every year, he makes the team and contributes. Just a thought.