The chemicals modafinil and armodafinil subjectively let me get away with a bit less sleep without the various consequences of caffeine. Used with enough sleep, they enter the realm of transhuman cognitive enhancer.
Also, when it wears off I very often get awful tension headaches and "mind fuzz", kind of like from caffeine but much worse. Unlike caffeine though, I can go a good 9 hours feeling energetic and only feel the pain once I get home and am done with the day, which is an advantage I suppose.
Interestingly, I also seem to get fairly powerful euphoria for about 2 hours after it kicks in, which to my understanding is unusual. (And yes, I'm sure what I'm taking is really modafinil.)
I only take it in "emergencies".