Hi, sorry if this is not directed at me but I felt I could give my 2 cents since I have lived in Halifax for a term.
My en-suite had a silverfish problem which is not uncommon in en-suite Halifax rooms. If you don't mind silverfish then Halifax is actually pretty amazing in terms of the events and support they have there. I have friends who loved it and those are the people who don't care much about silverfish (which is pretty much all of them lol). However, I did temporarily stay in a shared bathroom in Halifax and didn't discover any silverfish there (to be fair, I never looked down for long periods of time in there) so it might only be in en-suites.
Langwith is really good in terms of accommodation because it is a newer. I'm not sure what you mean by social, I haven't found Langwith to be anti-social in general, it hosts it own events from time to time and it has two other colleges on either side of it so you're close to any friends you make from east campus.
From the map from the uni, it looks like the department is somewhere behind/next to Alcuin so from Halifax you can catch UB1 to the stop after heslington hall (I forgot what it is called) and do a bit of walking, which will maybe take 10 minutes or if you're walking the whole way walking which may take about 20-25 maybe? It will be about 10 minutes or so by bike I think.. From Langwith, you can catch 66/66A to the library stop, and walk the rest which shouldn't take longer than 10 minutes.
In my opinion I would swap to Langwith if you can find someone willing to swap as it will be easier to commute, especially in the winter because UB1 stops around 7pm but if you have/buy a bike then it's not that big a deal. Halifax is not the ****-hole everyone portrays it to be but it's definitely not the best accommodation at the uni.
It's ultimately up to you and your preferences!
If you have any other questions, feel free to PM me