Hi Ellie – I suggest you might approach this in at least a 2 prong (forgive the pun) approach.
1.) Let’s Go – I would offer that you would introduce and develop this first with no distractions – then begin proofing the behavior with minimal distractions and progress up to all distractions. This will take some time…. Once you have a nice loose leash walk with no distractions – you progress from there. You want to develop and proof this under ideal conditions and then the world. Trying to do this with distractions and other dogs would make it hard to focus on what you are trying to accomplish and once both you and your dog are frustrated it can become a mess.
2.) The reactivity, or significant interest resulting in hyper-focus and moderate to extreme pulling at the sight of other dogs is a separate matter. I would be remiss not to mention however, that once you have a solid “Lets Go” where there is not constant pressure on the leash – you may be pleasantly surprised that the extreme pulling to get at/to other dogs may actually diminish. As handlers, we communicate a lot of information through the leash, our body language, and our voice tone and inflection, etc. It is common that a responsible owner, aware that their dog is a little iffy around other dogs, tightens/shortens the lead to keep the dog close in anticipation of what we know comes next. This may be the wrong message – unless of course the dogs are too close and there is danger. When we pull the dog in by tightening the leash when we anticipate a negative interaction, the dog may be receiving the message that we are nervous, anxious, or afraid so the dog does what it can to keep danger at bay. Similarly, you may notice that when another dog is walking their person (the dog is out in front of the handler and pulling) your dog may focus intently and then escalate from there. Your goal is to read your dog, and take action. In a natural setting it is not normal for dogs to meet head-on. They approach from the side which plays to their fight or flight, which gives the dog being approached the option to run away (flight). Robert’s videos on leash aggression/reactivity may be beneficial to see what that looks like if you have not been able to view them yet. Likewise, in one of his other videos he demonstrates how you can control 2 dogs meeting using a stacked greeting approach when you know the other handler and you control the meeting.
As to collar choice – my opinion is… handler preference. It is important that you are comfortable and if the prong is working for you and your dog, by all means – use it. Assuming your dog knows how to relieve the pressure on the prong – the choice is his to pull or not.
Hope something here is helpful as you make your plan and develop a loose leash walk where you both enjoy being out and about and enjoying your time together.