I think it ebbs and flows really.
For example I enjoyed our rivalry with Sheff Utd when Colin was there and also when we were competing with Wigan 10-15 years back - although that was based on the fact that at the time we were very similar clubs. But then times change and we moved onto West Ham etc
In the last few years I've been developing a healthy resentment of Fulham and their fans. Twats the lot of them.