You can be forgiven a few sins in non-sanctioned competitions, but in sanctioned the level/quality of the product goes WAY WAY WAY up. For a winning entry, each piece is darned near BBQ nirvana.
For us, we'd experimented with many sauces and a few different rubs and injections and had fair success. However, we finally had a big shin-dig where I started with 16 (as best I recall) base sauces and made the pork and briskets using 2 different injections (each) with what I felt was a very nice rub on each. I had 6 main taste testers, but another 6 lurkers. We snarfed and dabbled, this and that. Even for fun we took bets on which sauce would be the best. For what it's worth, we all lost. We ended up merging 3 of the base sauces. That combination works for us. It compliments the meat flavors and doesn't overpower it. Many of our favorite sauces ended up conflicting with the flavors of the meat and rub. Make sure they... marry, if you will.
For us, I make the sauce, then thin it down (using water). I apply it when it's VERY hot, with a sauce paint brush, very lightly so as not to rub the rub off of the meat. We then allow it to set up on the meat for 5 minutes.
That's what works for us. There are probably literally thousands of variations that work. Practice and you'll find the one that works for you.
Have fun. It's a journey; not a destination.