domain question what is better...

[Useless]

I think it all depends on the combination of words. How readable will the name be at first glance and can it be misinterpreted?

For example:
titsnass.com
titsandass.com
One may look like 'tits nass', while the other may look like like 'tit sand ass'. But I may very well be over analyzing the whole situation. I would just get the one that is easiest to comprehend at first glance. Oh, also think about how it would look as a graphic logo. That may help too.