You have more chance of finding a job in Bristol, because it's a larger city.  However, if your first choice is Oxford, why not try there first and, if not successful, switch your attention to Bristol.  As it happens, Oxford is on the way to Bristol; each leg of the journey is about an hour by train.

You could also try Bath, which is in the same direction, just before Bristol.  It is a very pleasant historic university city, which welcomes a lot of tourists in the season, so there will probably be jobs in hotels, restaurants, cafés, etc. available for the summer.  You could try the university for a room to stay.

Hi Marina, 

As a matter as a fact I know both cities, As Dan mentioned I totally agree with him. Bristol is pretty nice, and more to the locals, whereas Oxford is pretty inernational, a lot of students and it is not cheap. You might have to check the rent of a flat, because as I know they are quite expensive in Oxford. I was in July in Oxford for a while and have seen many caffees which were looking for a barman etc. 

I'm not sure when Amanda came to Bristol, but it certainly isn't dull. There are so many events going on a year like harbour fest, balloon fiesta, Saint Pauls Carnival, and many more, not to mention all the history, beautiful country side, vibrant nightlife, restaurants and shopping mauls.

It isn’t too far away from London if you want to take day trips. As for when the students leave Bristol is still active. Many student actually still stay for the summer holidays and work in the bar etc. There is still a large population of Brits living here, so you will actually converse with allot of British people on a daily basis.

I vote for Oxford!  I'm sorry Bristol but I think you're dull :( 

Bristol to work and Oxford to learn :-)