Hmm, I consider this a tough one between 2099 and Spider-Gwen.
Silk I don't see lasting beyond the first arc. I know Dan Slott says the character has demand and popularity but I just don't see it online. Now maybe offline and in pulls the demand is there, but until that shows up I doubt Silk will last beyond what it takes to collect a trade or two.
Spider-Woman's failed to stick before as well, and while they made a highly publicized re-design of her costume to try to appeal to the Tumblr crowd, I don't think that and Dennis Hopeless being the writer will be enough to keep it going either. I think it will make it to issue 12 but I doubt it'll keep going beyond that, especially if Secret Wars turns out to be a factor.
2099 has one of the best creative teams attached to a Spidey book ever and 2099 has enjoyed a bit of a resurgence in the mainstream eye lately. I think this one definitely has a good chance to get beyond issue 12. I definitely expect this comic to sell well for a decent period of time, at least until the creative team is changed. It's a well-worn concept (a man out of time and place), but David knows how to turn these venerable concepts on their head so I expect nothing short of a sustained quality comic. The staff is just a veteran, establishment crew with a good track record, and it helps that 2099 has been off to a good start so far.
If 2099 is the Boston Red Sox or St. Louis Cardinals of current Spidey comics, then Spider-Gwen is the Chicago Cubs. A wild card that has a fresh new lease on life after years, decades even, of being lost in the wilderness, but is relying on unknown variables. Gwen Stacy was the ultimate victim, deader than a doornail, now she is the hero and Peter is Gwen's cross to bear instead. The frankly amazing costume has a lot to do with her initial appeal, but Edge of Spider-Verse #2 is a legitimately great comic in its own right, and we are also exploring a new universe that if pulled off right can be like the early days of the Ultimate Universe, a comic of new discoveries and amazing twists. I think that if Spider-Gwen sells well from the outset and the quality of the comic is sustained then it could outlast 2099.
Regardless, I think both 2099 and Spider-Gwen will last beyond 12 issues. Who winds up lasting longer depends on what happens in the books themselves. Which is as it should be.