A wild suggestion
SPOILERS for: Buffy, multiple issues and Angel ATF Issue #3
I haven't gone through all the pages of this thread so I don't know if my screwy thought has been suggested yet, but I'm going to put it out there.
Willow
Isn't the first time we see Twilight in Issue 1, where the "˜shot' pans back and reveals just his feet as he suspends in the air? He flies. And what's Willow been doing since she moved over to comic land? Also, in the current arc "˜Time of Your Life', it shows that Willow went all black-eyed crazy again, and that she believes Buffy to be a danger. Why is Buffy a danger? A reviewer named "˜cylonpete' in another forum mentioned something interesting about a scene in Issue #14:
"What particularly fascinates me with the whole Season thus far; is the downfall of Buffy and her friends. They really start to behave like gods in their own right. Interestingly enough, the scene where they burn the vamp, reminded me not just a bit of a similar scene in Season 5's episode "Fool for Love". In the episode Spike tells Buffy how he killed two slayers, one of them in China. Spike, Angel, Darla and Drusilla leave China in the exact same manner; and Spike walks in Buffy's spot. Buffy is disgusted that Spike enjoyed the killing, but here it appears to me that she did the enjoying. Mhm. No wonder Twilight wants to snuff her.;-)"
Maybe Willow sees Buffy & the other slayers in the same light the military does "“ as a threat. Only Willow has noticed it from the inside.
Also two smaller, and maybe insignificant, things "“ in "˜The Long Way Home' arc Buffy had that dream with Ethan Rayne and then later, I think in the next issue, Willow says something that was mentioned in the dream. Buffy looks up and has this "˜Hmm' moment. Not sure if it was explained where that led to, if it was there to help Buffy realize something in dealing with the current situation, but if it didn't it could imply that Willow knew of the dream because it was intentionally given to her, and if that's the case she could be Twilight. Also, Willow came out of that torture session with Warren way too unscathed. I know it's implied that her magic saved and repaired her, but something about it seems a bit suspicious.
Now before you say, "But Twilight's a man!" remember that glamour spells have been used plenty in Buffyverse (such as Angel using one to still look like a vamp in his book), so Willow could be using one to make the "˜man thing' happen. Notice that even Twilight's voice is "˜masked' by the use of different script to imply his voice is altered.
I'm down with all the other good suggestions "“ Riley, Xander, or even Buffy's dad (although where did any of them learn magic?), and Giles. I'd also agree with Angelus, Spike or even Caleb because of that, "I've seen that move before" line. Hey, it could even be Oz, especially since I read that he'll be appearing in an upcoming Jane Espenson arc. Truth is we can all speculate like crazy, but the only one who really knows is Mr. Whedon, who is probably visiting forums like this, reading all of our banter and smiling his ass off at all of our wild guessing.