Dante-
I'll give you the punchline first...My ideal poker site would probably take Pokerstars software, tournament structure, and customer service and combine it with Party's clientele and cashouts.
I used to play at Stars when it was in Beta testing and played there periodically whenever they offered bonuses (why not get a few extra $$ for something you would do anyway) once they went live. Additionally, I played there for a few of the larger tourneys. With that said, the games at Party are so good I have a difficult time playing at Stars and once Party started the HUGE tournaments on Sundays there was little need to play at Stars.
In another post a few months back someone asked a similar question regarding Stars and my response was that I find it difficult to play at a place (Stars) where my EV is lower UNLESS it offers something substantial. Another way to think of it is if you have accounts at both Pinny and Oly and they offer the same line on a game, would you play at Oly at a higher price? I wouldn't. While the software and service at Stars is TOP NOTCH and PARTY is pissing me off with their software problems, I can't imagine voluntarily playing in tougher games. I don't need to "test" my skills, I know where I am.