Hello both!
It would be easier if you had any specific questions, but for now:
I am a second year undergraduate and I am at Aidan's (but live out in my second year). St Aidan's is actually a wonderful college. Whilst it will seem enormously different to Josephine Butler (not self catered, possibility of shared rooms) I think the better to way to look at it is Josephine Butler is different to pretty much every other college in Durham. Only a very small proportion of students self cater in first year. Aidan's, like the majority of colleges (in Durham city) is catered, but the food is usually reckoned to be good. There is plenty of choice and while people always complain about it, it is of a high standard considering it is all mass catering. People also find making friends is easiest in colleges with catered food as you can meet everyone in college easily and share meal times with them, rather than being separated off into flats. Josephine Butler has its own stereotype of being elusive and less involved in Durham life, partly because it seems so far away and partly because it is so different.
In other aspects it is quite similar. They are both Hill colleges and so their location is similar. Aidan's is actually closer to where you'll be doing lectures and despite the hill is a really good location (plus have stunning views). With regards to college life/ spirit, every college has it's own JCR and organises its own events. You're lucky in the fact that Aidan's has one of the better JCR's - it is very active. Aidan's is also known for being one of the most friendly and inclusive colleges where everyone feels welcome. It used to be known as 'the party college' but this is now not the case, although it is less traditional than other colleges. There are no gowns (due to historical tradition - Aidan's was the first college to admit women in the university and they didn't want gowns) but I would argue this is a good thing. It means all of our formals are different. We have smart, black tie formals, but also huge fancy dress formals. You can attend a gowned formal at another college if you want the experience, but lots of people find it is nice not to HAVE to wear a gown - the first time is fun, the next few times you realise how expensive it was, how hard it is to keep clean and they are not comfy. You can't even graduate in them. Most people enjoy it as an experience, but dislike having to wear them after that. Aidan's bar I also prefer to Butler. It always has people in and lots of social activities go on there. Butler has a reputation of being a bit like a bus shelter.
Until you get here you wont really appreciate it but whichever college you end up in you will love (and will automatically claim it is the best college). Each college has it's own character (at the moment) and it's own unique atmosphere. I'm sure you'll end up loving Aidan's as it is easily one of the most friendly and inclusive.
Do come on the post application open day though, it really gives you a sense of what life will be like at Aidan's and most people LOVE it
*Also you'll discover you're not alone, loads of people get reallocated to different colleges. It's because they try and have a balance of all different subjects at each college and people always tend to apply to the same colleges, either University (because it's a castle) or Jo Butler because people think they can't live without an ensuite!