Of all the Amigas I owned I think my favourite would be the A500, simply because it was my first ever Amiga, and it gives me the true 'old school' Amiga feeling.
Runner-up is my A4000/040. It is the dream machine I could never afford back then, but I have bought it last year for very little money. It's nicely expanded now and can do more than I ever dreamed of 10 years ago.
Third comes the A3000. It's not as fun as the A500, not as 'killer' as the A4000, but in my opinion it's the most beautiful Amiga ever made. I still regret the day I gave my A3000 away for practically nothing (I'll buy myself one again someday).
