The SP because it was so much better than the rest. 

DSi for me.

" The SP because it was so much better than the rest.  "

DS lite it plays DS and GBA games.

SP did it all.

well i put GBA but i guess DS because they play GBA games and DS games, a few of which i like

Gameboy pocket.
It's more nostalgia factor for me though.

i love gamboy

gotta go with the SP, it's still the coolest looking gameboy to date

DS, and the PSP are the only hand held systems I personally have ever owend, and I like the DS more.
 
Also, you shouldn't have separated the DS, DS lite, and DSi, they should have been the same choice.

Ill go DS lite since it can play GBA and DS games. Although the GBA can play Gameboy games.... so i might have to go with the SP.
Hard choice....

I put DSL because it was the first handheld I've ever owned from Nintendo. However, I have fond memories of the fatass grey gameboy and it's younger brother GBC.

Easily the Game Boy but it's even better when it's yellow :p

GB Micro, surprisingly fun given the size. GBA SP is a close second. The DS Lite has some great homebrew music apps but the games just weren't my bag.