Hmmm. Of the ones I own I think the older ones tend to be the ugliest. Intellivision and Colecovision are just too boxy.

Having just gotten an O2 I will say the first thing I thought was "jeez - this thing is as big as an Xbox" (though not nearly as heavy).

The Xbox is just big - and I like the green/black colour scheme. But it's not my favourite.

As for best looking, I'd go with Dreamcast and Gamecube.

I don't hate PS2, it just doesn't do it for me. I have to agree that the PSone looks pretty slick too (but I still go with DC and GC)