i find both have a distinct difference....If you like the city life then oxford is your place. I know i dont like this lifestyle, because i have been in central london at 3 in the morning quite a few times, and everyone is drunk and it's all really busy and everyone is throwing stuff around and generally i just dont like it.
If you like the town life (with a pop down the local for nice chat) then cambridge is the place! I personally much prefer this type of behaviour.
Now don't get my wrong, both places can offer both of these lifestyles to some extent, however the above is more of a generalisation. As pointed out above, oxford does have more clubs...but clubs just arent my scene, so the fewer clubs the better imo