Hands down, no contest, best bang-for-the-buck is the Audio Van Alstine FET Valve 550EX. Detailed, dynamic, gobs of power, and handles loads down to 2 ohms (are you listening, Apogee owners?). It's non-fatiguing and plays very well with any speaker I've tried it with. Puts amps 2-3 times the price to shame.
Lovin' every minute,
Ed
Lovin' every minute,
Ed