My favourite Handheld?
I love all of them, but 3DS is the best at the moment.
Main reason is, it's a handheld where they will focus on hardcore gamers again, and the DS Market has been killed by piracy.
Gameboy Color, Gameboy Advance, and the DSi. All fun and enjoyable. They all also hold a special memory for me. Not all of them are brand new and amazing to most, but they are still special in my opinion.