I'm going to go back to a set of classic arguments here--I voted for Kiki, Tendrils, and Warp World, for three different reasons.
Kiki and other two card combos, especially with cards that just aren't excellent on their own, are not my cup of tea because they're overly centralizing. In reanimation (which I think you should add to the poll!), it doesn't matter if you're reanimating
Griselbrand or
Elesh Norn or if you're using
Animate Dead or
Reanimate, there's a lot of different ways to use the parts and you don't trainwreck your draft if someone else speculates on the combo. (Offramps into
Sneak Attack or
Goryo's Vengeanceare perfectly respectable) Also, a lot of specific two-card combos make the draft very experience-dependent, meaning that people will either not understand what these cards are doing in your cube or, upon seeing
Pestermite, will assume you have a Kiki-Jiki and draft accordingly only to be frustrated when they find out at the end that the combo is simply not there.
For Tendrils, it's really hard to interact on the stack, meaning that there's not much you can do as the opposing player besides try to kill them before they bonk you for a bunch of damage out of nowhere, which brings me to another big gripe I have against combo--it oftentimes is very difficult to anticipate what combos you might be playing against, especially in a new cube, meaning that you're even more taxed in terms of counterplay. For aggro, midrange, and control, it's generally easy to figure out what they're up to within the first couple of turns and to assume either the beatdown or the non-beatdown position according to that deck and yours. Furthermore, the goal of the Tendrils player is to assemble the combo as quickly as possible as they've generally made significant sacrifices in terms of what their deck is capable of doing to do so, making it very feast or famine. I'd love to see a deck that uses Tendrils as a win-con after aggroing someone down to 6-10, but generally it's hard to make a deck that starts offensively and then transitions hard to a defensive spellslinger stance. (I've been inspired by
Mizzix's Mastery, though...) Door to Nothingness doesn't bother me as much because it's both very expensive and restrictive (10 mana!!), and is highly interactive, usually sticking around for a turn cycle and offering a target to be removed unless you get to fifteen mana, which probably means you've won anyways. I wouldn't include Door because I think it's usually a trap, but I'm totally fine with losing to it and would actually be impressed.
Warp World, on the other hand, is loss by randomness. If I'm going to lose to a combo, I want to see fireworks going off, not a series of coin flips.
Again, these are not new arguments, but I think they're pretty standard for a reason. I'm fine with mill because usually it's both a double-edged sword in my cubes due to there being significant play from the graveyard and it not typically being supported. Again, I'm not a fan of dedicated mill cards and probably wouldn't put that in my cube (e.g. I would play
Didn't Say Please but not
Tasha's Hideous Laughter), but there are a number of otherwise playable cards that offer decent counter play (
Loaming Shaman, etc.) so I think it could become a decently competitive theater to play in if a cube is designed with that in mind.
Burn is a subset of aggro for me and is kind of inevitable with enough red removal. Besides, normal Magic involves managing your life total anyways, so there tend to be more options in the sideboard to deal with this sort of thing than there are for mill.
Finally, labman dies to removal. Thassa's Oracle is a little more suspect for me because it doesn't, but generally speaking these creature-based combos are easy enough to interact with and tend not to win the game the turn cycle you play them, so I'm more okay seeing them.
Going back to my point about expectations, something that's very important to me are the expectations your players have about how they need to use removal. If a player is using it "intelligently," by using removal on key threats, I don't want them to be punished for doing so by whipping out a combo that wins on the spot. While big creatures offer a comparable "remove or die" challenge and can also be exploited by trying to run your opponent out of removal, they're often some combination of obvious and slow. Baneslayer Angel requires a full turn of setup and often needs two or three to actually win, as do many massive threats, whereas combos tend not to offer either that sort of window or that type of interactivity.
