I've used the DT Systems and several Tri-Tronics collars. Keep it simple, the tri-tronics 100 mentioned by victor charlie is a great one. Main thing to remember, more dogs are ruined with them than made. Unless your breaking a dog off undesireable game, they do not train a dog! For training,,,breaking a dog off game it's used as a form of severe punishment. I've used them to snake and porcupine break dog's but it's is punishment and work's.
Avoid the collar's with all the good boy tone's and be carefull tone's, they are confussing. Also avoid the collars with a delayed shock, very had to time the shock correctly; timing is everything. The Tri-Tronics 100 is a great one. You can have constent shock or 1/10th second shock; no bells and whistles. You don't really need one with a 1 mile range either. If you can't see your dog, there's no good reason to shock it.