There are 1072 bedspaces in Northfield, 575 in East Slope, 474 in Stanmer Court, and the rest have around 250-300 or so (not to sure about Park Houses or Village though).
I would've chosen Swanborough because it looks nicer than Northfield and it's in the centre of campus, but due to that, I'm guessing its going to be well-oversubscribed considering they only have 250 bedspaces. If you have an unconditional offer, or you're an international student, then chances are you will get your number one preference. If you're a domestic student with a conditional offer (like myself), then just hold tight
but Northfield is supposed to be their biggest on-campus accommodation in terms of availability, so fingers crossed. Also, don't forget that it's the furthest away from campus out of all of the other on-campus accommodations, so that might put people off too. If you don't get the accommodation you want though, there's always the chance to do a swap with someone when the swap-lists are available, as much of a pain I know that is.
I've put down Northfield as a top choice myself - I'm willing to take the gamble. I'm really not keen on East Slope or any of the other shared-bathroom accommodations (apart from Brighthelm), purely because I like my privacy when washing myself or using the toilet. Plus, the thought of walking in the same corridors we throw parties in, in my towel after a shower puts me off a lot. Anyway, I know you didn't really ask much and I'm just over-detailing it now haha, but I hope that's helped a bit