I LOVE the GBA. Best handheld of all-time. So many great original games, so many great ports of 8-bit and 16-bit titles, and FINALLY a backlit screen on a Game Boy! Plus it's backwards compatible, opening up an entire new library of games that look even better on the GBA with the backlit screen than it did on the original hardware.
My least favorite console, that I've actually played, is the N64. I just HATE that controller so freaking much. And I don't like that it's missing RPGs and shoot-em ups, my two favorite genres.
I know there are much worse consoles out there, but personally, I haven't played most of the super-rare consoles like Pippin or Atari 5200.