I'd only use a gentle leader or halti as an absolutely last resort. It renders a dog completely helpless and they know it.
It is incredibly effective (from the human's standpoint) for that very reason, and because it appears not to cause pain, it is considered an acceptable level of restraint, but often produces a significant change in behaviour, one I characterize as 'humbling'.
If you chose to use one, 1st you need to condition your dog to accept wearing it. Dog learns to associate wearing it with getting treats.
2nd. I highly recommend also teaching the dog to associate light directional pressure on the leash with getting a treat from the rear flank (so he doesn't freak out when he wants to go one way and feels leash pressure from the opposite direction.
3rd. Go out with a light line or tab on the halti and regular leash on collar, continue the conditioning (treats for gentle leash pressure), and work your way very slowly (over several days) to controlling your dog with a halti.
4th. Bear in mind that if your puppy or dog is given to flinging itself to the end of the leash to chase a squirrel or car, whiplash can result.
There is no collar I've ever used that is so difficult for a dog to accept, but if you absolutely have no other options, then the above steps will help your dog.
If choosing between halti or harness, then yes, harness, harness, harness, harness, please.
If you're own safety becomes a factor (sore muscles, tripping hazards, getting pulled around, sprains, shoulder/back injuries) and a harness doesn't work, there are other options that are less upsetting to a big boisterous puppy.