What centre

The one that operates in your area should be your first choice if you intend to rally. If you find you don't like it and don't mind travelling further afield then perhaps some of the adjacent centres to your area. Of course if you don't intend to rally regularly then it doesn't matter which centre you join or even if you need to bother.

peedee

You don't have to join a centre to go on a rally. We tried a few rallies with different centres before we joined a centre (not our local one either.) So if you think you might like to try a rally have a look at what's on offer.

Look at where each centre holds their rallies and choose the one that goes to the area(s) where like to go the most. Probably worth taking Brue's advice to try a few different centre rallies before making up your mind.