Campy, Shimano, SRAM I think this is a personal choice as all work well. There is a difference in comfort and operation, but again they all do the job well and you won't be disappointed with any of them. Price is a real consideration between these mfgs.

If you don't have your position dialed in yet, I would suggest a frame with without an integrated post. There is some adjustment, but not a lot. For many this takes some time to get it just right and the freedom to move the seat may make all the difference in a perfect fit or something close.