I am also on a 2020 freshers group chat, where everyone says what they are studying and what they have applied for accommodation wise etc, and 85% of the group chat said East Slope was their top choice. This makes me think that the social life can't be that bad, as it seems to be everyone's top choice from what I am aware of! Northfield is apparently a mix, half with international people etc but also decent social life. The only downside is that is can be seen as quieter as it is a good walk from the main campus! However, the actual accommodation is nice enough. Personally, although I am a party person, I am prioritising the cleanliness of the rooms and space etc, as I can go to parties in other cheaper more run down accommodations, where personally I couldn't live as I am very fussy!
However, I'm sure you will be happy wherever uni is uni and you'll make friends regardless of where you are living x
Hope this helps x