The gentle leader head halter can be a very effective tool in the right hands. It has the benefit of directing the dog's head to where you want it (like facing you instead of the other dog) and it also closes the mouth which helps prevent biting. But there is usually a period of time needed for a dog to adapt to it, and many "attitude" dogs have a hard time with this because they don't WANT to be restrained and head halters are very restraining.
The e-collar has it's place too, but using it for aggression can have bad results if not done with a great amount of skill and knowledge. What you don't want is to have your dog learn to hide his aggressive side because he doesn't want shocked - you want to teach your dog control without building hidden aggression. I've seen dogs who learn to hide the aggression and it can build up and explode at random times (which is really scary, having a dog that shows no signs that it's going to have an aggressive rampage).
If it's control at this point that you want, I would suggest looking into the gentle leader HARNESS instead (or any of the harnesses that have the ring for the leash on the chest strap. This harness will help guide your dog around away from the other dog and back to you without engaging his head and making him fight the restraint. And then I would suggest doing some desensitization exercises at a distance from other dogs so that he learns that controlling his impulses results in good things. Then you gradually work closer to other dogs over a period of time, instead of expecting him to be up-close and in control. I've had really good success with students doing desensitization.
If he's highly dominant as you mentioned, I would also recommend a lot of rules and boundaries. He shouldn't have ANY privileges if he's thinking he has the right to be dominant even when you say he's not to be (like when he acts aggressive toward another dog in your presence). Use NILIF and control every single thing in his life - his food, his treats, his toys, his access to outdoors, his water, etc. When he has to look to you and provide you with behaviors for everything he gets (well, air is still free) then he will start to view you as a leader and as someone who has the right to say "no, you can't act this way".
Good luck!
Melanie and the gang in Alaska