From all the posts I've read here, from what I've seen on horses around here, from clinics I've been to -- the most important thing is the quality of the trim --your regular farrier may or may not be the right person to go to for barefoot work. Ask around -- who else is barefoot around you? What do they like/not like about their trimmer? How have their horses transitioned?
Also, generally speaking, a barefoot trim makes the hooves stronger. So even if your horses have cracks, chipping etc... go for the barefoot. Chipping, for example, is generally a sign of a hoof being too long so it's trying to "fix" itself.
I don't know what the rules are in competitions, but I can't recall anyone ever saying they HAD to have shoes in the shows.