For me, poker stars are the best poker rooms in general. There is a lot of online, there are a lot of tournaments, a lot of games that you can play, the interface is beautiful, the graphics are excellent. Poker Stars has everything I don’t know why someone else chooses where to play.
I think both sites are very good, they have great tournaments, quite a lot of player traffic and very reliable ... however I like the pokerstar interface more ...!
It really depends what you're looking for. If its large guarantees in tournaments Poker Stars wins by a mile. If its rewards and cash back Party is likely better. For spin and go's Party is going to offer a higher payback and lower rake. If more rake is better then you want Poker Stars. Poker Stars software runs a little bit smoother. Neither can hold a candle to GG Poker's software.
Both are very good and respectable sites. You can’t really go wrong with either one. I think PokerStars has a better App with more selections if you play that way like I do. I can hardly find any tournaments on the party poker app nor the 888 app compared to what you find on a laptop/desktop.