Hullo alexsandra, I don't kow whether i can really help but here it goes...
I'm planning to go to sussex also this year (english and media studies) and I was also considering the three you have mentioned and put them in the folllowing order: east slope, park village and then park houses.
I chose east slope because it was the cheapest but also because it seemed really nice and friendly when i visited and I liked the layout of it. Also i think it's in a good position on campus. Park village was next and i like the sound of this one but the communal area seemed to be a bit lacking in that they have no kitchen table, so there's not really a place you can sit around together (however this may not bother you).
To be honest i would'nt mind living in any of those three and it probably won't make much difference. You'll just have to go with what will suit your needs/wallet.