At the time, I was madly in love with the original Gameboy but I know it was vastly underpowered and had a fuck-ton of shovelware. I wasn't as hyped about any Nintendo handheld until the DS which I quickly got over when I got a PSP. Now, the 3DS has taken over and it won't let go. I play the 3DS when I'm home with my "Big boy consoles" so that has to stand for something.
I'm gonna say 3DS. Not just because it's the newest but because I love it and it loves me.