A good dog is hard to beat... I have used Blueticks, Catahoulas, and even an Australian Shepard over the last 30 years. I have a Catahoula "Belle" now that is a retired hog dog that is the simply the smartest dog I've ever owned, she always seems to know what her job is. Belle does not need a leash or tracking collar, she's patient and waits on me.
The little dogs are great until they have to stop a wounded buck, or doe for that matter. I hurts to loose a little best friend. A wounded deer can be really rough on a small dog. The good news is their nose is just as good as a big dog's and if kept on a leash there's never any real danger for the dog.
I have never had much luck in heavy rain, be it hog hunting, coon hunting or trailing wounded game. I have found some close trails, but in my experience the more water on the ground the worse the chance, but that's just my experience.