I tend to choose domains on both the aesthetics of the name itself, not having two of the same letters next to each other in the domain is a big one for me, also the brandability (is that even a word? LOL) of the domain.
I also like two word combos for surfer orientated sites wherever possible
Other than that, traffic can come and go, just because a site gets 100k hits a day while a domain is being or has been owned by someone else, that doesnt guarantee the same 100k of hits will be there if we buy the domain.
They also have to be .com without any exceptions.