Some great insight here.
I've done both the dog and the child at contests and I really think dogs are easier, plus some people get upset seeing your kids on leashes! The last time I had a dog at a contest was the final day of the '89 world championships. I had my Chocolate Lab, Bailey, with me and he was always friendly and well-behaved. I was having a nice chat with Sally Brown while Bailey sat behind me, on leash or so I thought. Bailey had quietly chewed through a 1" nylon strap. He didn't go far. About 15 feet, in fact, where he had pulled over a garbage can and had almost completely disappeared into it rummaging for food. What a happy dog! At best, dogs are maybe 99% predictable; so just make sure you account for the other 1%.
I can't imagine life without a dog or 2 or 3... and a few cats, too!