Each GC has different gear. Generally there's a good piece for each job, but different pieces are going to be good for different jobs. For instance, Uldah has the best GC body for BLM (currently) and Gridania has a good body for BRD, DRG & MNK (though AF may be better in some cases.)

Ultimately though, I'd say choose the GC you like best. You'll be able to get useful gear from all of them.