Some years ago I read The Intelligence of Dogs by Stanley Coren. What I remember is him saying that what we consider intelligence is really trainability. Back then I was heavily involved with horses and didn't really do a lot of training with my dogs, but I do now. A friend who also trains and competes with her dogs refers to it as whether or not the dog is biddable.
So just from what I've seen, there are dogs who are quite smart but not biddable. They can, for instance, figure out how to open doors and do other things that entertain or benefit them, but they aren't keen on doing things they consider stupid just because some human wants them to. I'd put the Akitas I had in that category. I wasn't doing any real training back then, but I still smile remembering the one, who when called from a distance would not just ignore me, but would stop and look back over her shoulder as if to say, "Yeah, I hear you, but I'm not coming, so stop wasting your breath."
Other dogs aren't actually that smart, but they're very biddable. They're easier to live with because they couldn't figure out how to open a door or get into other kinds of trouble to save themselves, but they're quite willing to repeat some obedience command 50 times in a row if it pleases their person and/or results in a food reward.
And of course some dogs are both smart and biddable. But in choosing what's right for you, you also have to consider other traits. For instance, my Rotties are very biddable, but one of them is also very high prey drive (not uncommon in the breed) and very motion reactive, not a good choice for most people as a first dog to train. Some others from highly trainable breeds are so high energy they'd be difficult for a lot of us to live with.
Here in Colorado I'd guess the most numerous breed in the obedience rings is Golden Retriever, but there's also always a good representation of Labs, German Shepherds, Rotties, Aussies, Border Collies, and Shelties. Some Poodles, Corgis, French Bulldogs, Bernese Mountain Dogs, Newfies, German Shepherds. Of the terriers, Border Terriers seem to be the choice of many.
There are always fun and interesting surprises. At the last show I went to, I talked to a girl with a Swedish Danish Farm Dog. I once saw a Miniature Dachshund knock everyone's socks off in Rally.