1. Commodore 64
2. Commodore 64
3. Comm... just kidding!

Seriously though, here are my top 10 based solely on the systems I currently own:
1. Commodore 64
2. Atari 2600
3. Colecovision
4. Amiga CD32
5. Genesis
6. Intellivision
7. Atari 5200
8. VIC-20
9. PSX
10. Odyssey 2