Where to Begin?
Wonderful! Beginning competition is really exciting for you and your dog! As to what organization, there are several things to consider when choosing an organization, and everyone has a favorite, it seems like! I suggest trying as many as is feasible given location and funds, and if you really really REALLY want to do trials that aren’t in your local area (such as NADAC, or for those with little dogs, TDAA!) you might want to start your own club. If you’re having trouble locating local trials, try googility.com – they often have great local resources!
I have heard good things about all the organizations, although experiences vary. I think your best bet is to just wade in and try a couple different ones, or talk to your trainer to find the best fit for you and your dog.