I had a VERY strong willed dog that liked to pull. I could train her back for a while but it required constant correction and walks just weren't pleasant. I tried both a prong collar and an electronic stimulation collar that I activated when she pulled. Neither worked very long. I had the best success with a Halti. It's like a harness and it turns the dog's head when they pull. Worked great and doesn't hurt at all.
The other thing I was thinking of trying was a whistle they make that goes off when they pull. It distracts and confuses them.
Leash Whistle
Halti