Does 'Destiny' even belong here? It isn't "upcoming" after all. Anyway:
-Doom: Meh. Never got into the series, and for FPS's of that era, I hold 'Marathon' as a superior example. What may have been shown at Quakecon is irrelevant as no-one who didn't go saw it, but based on what I read..."meh."
-Halo 5: Far too little is known about this for me to comment - at least with 'Doom' I have an idea of the playstyle. Besides, 343 poisoned the bucket with 'Halo 4' for me, so no, I'm not voting for this.
-Unreal Tornument: Don't care.
-Far Cry 4: I've only ever seen the intro trailer, but it was enough to pique my interest. I doubt I'll get it or any 'Far Cry' game in the near future, but for what the series is, and what it's meant to be, I think it looks like a solid entry in said series.
-Rainbow Six: Pretty much 'Far Cry', but less enthused. Happy for this genre to be back, but it's not a genre I've ever gotten into, so...yeah.
-Star Citizen: Not an FPS, and I'm wary of the game in general, so...yeah.
-Killing Floor 2: Never heard of.
So, yeah. One big "meh." I think of all the above options (not counting 'Destiny' as it isn't "upcoming"), I'd go with 'Far Cry 4'. Ask again when we know more about 'Doom' and 'Halo 5' and they'd probably be the most logical contenders for me. Main guideline for me is for an FPS to have a strong singleplayer element (hence the lack of interest in UT for instance).