I also have used a prong collar (not on a puppy) when I needed to fine tune that pulling/heeling.
Sinister is a year old in your avatar, so a prong would be ok for him at this age if that's the way you decide to go.
Something else, work with him daily on the no pulling, my method of teaching a heel or atleast no pulling, is, if they pull, immediately go in the opposite direction, SAY NOTHING, keep doing this when they pull or lag alot,,when the dog gets into the position you want, (i want a left side heel), praise to the heavens "good spot, good heel",,(whatever you use for a command).
Granted, ya might get mighty dizzy changing directions, but if your consistent and say absolutely NOTHING until the dog is in the position you want, it does work
) Also walk like you are on a mission, stand straight, and go
Don't fall down