I was at Butler from 2018-2021 - it's brill! There are always certain stereotypes / horror stories about all Durham colleges, but I genuinely can't think of anyone who had a bad time at Durham specifically because they were at Butler (which has been the case for some of my friends at Hatfield, Stephenson, Trevs, etc.). I put it down as my first choice college and got it, but I know a lot of people who got allocated elsewhere and made a request to come to Butler.
It's got a lovely bar and social space, and it's the only college where you're guaranteed your own room with an en-suite. Plus, it's the only college that's entirely self-catered, which I think is a massive bonus.
There are some downsides - for example, the 'library' is a bit rubbish (but imo, no college library is really that great and pretty much everyone will rely on the main university library at some point because of this). Other than this, I can't think of any major let downs at Butler.
Some people are after the 'Durham experience', meaning white tie balls and posh formals etc. - Butler lacks in this department a bit, but I view that as a good thing. The college still does regular formals and balls (maybe a formal a month?), but they're usually a bit more relaxed and have fun themes. They're also are WAY more affordable than other colleges - when I was there, a formal including a three course meal and a glass of wine cost roughly a tenner. It's a nice way to indulge in posh Durham culture, but also poke a bit of fun at it with fancy dress and stuff like that.
Also, because it's the cheapest college accommodation (I think?), it tends to attract the more 'normal' students. I'm sure you're aware that Durham Uni has a bit of a reputation for being a bit elitist - in my experience, you're way less likely to encounter snobs at the newer colleges, like Butler. This might not be important to you, but I found it really integral to me enjoying my time at Durham.