What fuels can turbofans burn? I know that Jet-A is the fuel most often used for turbofans, but is there something else that these engines can burn? (ethanol, LPG, methane, butane, 100LL, etc.) Basically, can a turbofan burn anything, or are there limits in terms of temperature, combustibility, and so forth? also, which fuel out of any you can think of would be the most powerful/fuel-efficient?
As explained in Why do jet engines use kerosene rather than gasoline?, turbines can burn almost anything, but the lubricating properties of kerosene make the fuel pump simpler as it is otherwise hard to keep high-pressure pump lubricated.

Temperature limiting is simply a matter of sufficiently lean mixture and cooling air stream along the combustor walls.

And most efficient depends on criteria. For money it is definitely kerosene (Jet-A). Actually, Jet-A is an excellent match overall. It is relatively dense (~0.8 kg/l) while still having good specific energy (~43 MJ/kg; so fuels tanks are not too big), lubricates (good for fuel pumps), has quite high flash point (low risk of fire when handling) and is a large fraction of crude oil (C8–C16 (gasoline is just C6–C8) so it is cheap).