The best? Take a look a nmaher's Menace, designed with Pete Millett. Gilmore's Dynamight, or a four channel Beta22 are also excellent. If you like minimalism, take a look at Ciuffoli's SESS - my next project. If you really want to go for it, ask Frank Cooter for some of his schematics - his amps are incredible. You can also clone any number of high-end commercial amps. It might take some digging to find schematics, but many of them are out there if you know who to ask.
Anyhow, what are you looking for, how much do you want to spend, what are you comfortable working with, and what's your associated equipment?