I've cooked on both a Backwoods Competitor and a Pitmaker BBQ Vault. They are both great cookers and you can't go wrong with either one. You see less Pitmakers at contests mainly because they haven't been around that long. I haven't had any temperature control issues. I usually use a Guru but I have cooked without it. In our last 5 contests of the season we won 3 grand championships and one reserve.
The main difference between the two cookers is the method of construction. The Pitmaker is made of 1/8" steel and all seams are welded. The BWS Competitor weighs 350 pounds and the Vault weighs 850. Yes it takes a little longer to get it up to temp because it takes awhile to heat up all that steel. I always use water in the water pan mainly because that is what I was used to with the Backwoods.