Greatest Handheld?

Over the years there has been a lot of handhelds released.. The ultimate question is which is the best? There's been Game Gear, Gameboy, Gameboy Color, Gameboy advance, Playstation Portable(PSP), Nintedo DS, among others. You're saying, "Over the years technology has improved.. Better quality.. Better graphics..", etc. This is true.. But who doesn't enjoy playing some classic games on Gameboy Color every now and then? Which handheld do you think is the best? Do you like the new age systems, or the classic systems?