Something no one's mentioned (or my brain is broken) is that Stars' SNG tables are 9-handed, which makes winning less profitable than at Party, even with the lower rake.

Also you start with 1500 chips to Party's 800, the chips-to-blinds ratio is higher at the start (IIRC), and the players are slightly better, so games take longer, reducing your hourly take further.

On the other hand, it better suits some people's playing styles to have more chips to work with. I find that I consistently cash more often at PS.

All things considered, I'd usually rather give my money to PokerStars, and they have a special place in my heart as the site where I built my BR from low double digits, playing .05/.10 and .25/.50 limit and $5 SNGs.