The dogs and I have competed in AKC (obedience, agility, rally, tracking, conformation), USDAA (we did Junior Handlers and then very few regular trials), APDT, UKC (obedience, rally, conformation), CPE (just a couple trials), CDSP (just a couple trials), and NADAC (what we did the most of).
We did a lot more NADAC than anything else for a few reasons; 1)Most of my classmates did agility... I liked knowing people at trials, 2)I really like(d) the concepts of NADAC.
I still bring Buzz out for our APDT trials to play in veterans if he's feeling up to it but we haven't done anything other than that in years now!