At this rate, this thing will never take off. We need to note that any level we pick will subject us to the same level of power, except in the form of pure levels of classes. I suggest that we do not exceed level 12 for all purposes. Resurrection and quickened spells favor the PCs too much, unless we go with a low ECL creature. But if we go with a low ECL creature, what is the difference between that and playing an evil PC? Nothing!
I'm favoring the mindflayer, but with very few levels to play with (i.e., 4 or less). Out of this list, I feel that only the following are really playable, while keeping this campaign true to its unique nature.
1. Mindflayer (+8 ECL)
2. Yuan-Ti (+7 for pureblood, +9 for half-blood)
3. Vampire (+10)
4. Medusa (+6)
The others (and the vampire is almost one of them) have too high a ECL to be played effectively, or else too low of one, if which case we're just building evil PCs (no fun, IMO). I still favor the mindflayer with 4 levels! I don't think that we should worry too much about the other side min/maxing too much (after all, Janos Audron is on our side and I think he's probably the biggest min/maxer on this board...no insult intended).