I'd say FWD is the best because (at least in cars with the engine in the front) there is more crap to get the power to the rear wheels in RWD. I think the rule of thumb for drivetrain losses is 15% for FWD, 20% for RWD and 25% for AWD. I might have the AWD and RWD confused though, but you get the general idea. I think RWD might be better if rear engine, but in that case it might not matter.
FWD cars also reach full drive train operating temperature quicker, since the works are concentrated in one area. on a rwd/awd vehicle, the rear part of the drive train (differential, axles) don't benefit from the heat of the engine compartment and so don't warm up as fast (= extended period of losses from higher lubricant viscosities in those components).
Definitely FWD. Not only do RWD/AWD vehicles have power losses and do no not warm up the drivetrain as effectively, but also the components weigh more.
An FWD vehicle usually has the transaxle integrated closely to the engine and half-shafts to the wheels. RWD vehicles have a long driveshaft and a differential at the rear axle, and AWD/4WD vehicles have the added weight of the above and a transfer case or similar.