For me?
The Battle Royale GBA SP of course!

I also love:
>Rayquaza and 'Bob GBA SPs
>MOTHER3 GB Micro
>PKMN Dialga/Palkia & the Giratina DS Lites
>Majora N3DS
>Fucking Machinima and Taco Bell 360s
>Net Yaroze PS1
So many cool / weird Game Boy and 360 ones.