After purchasing our car, we fought with the original style pump for quite a while and could not get it to stop leaking. Changed to a leakless pump and have not regretted it...well, not yet at least. I suppose inexperience and a worn out pump were probably the biggest culprit for our lack of success, but the leakless has served us well and it has been nice to not have to keep repacking it every couple of months. When selecting a pump we opted for Snyder’s A-8502 as you can supposedly pack it like the original in the event the seal fails.
If the pump in question is for the car in your avatar, it is my understanding that you are running a B engine. If that is the case, I do not think you have a leakless option, so packing might be the only way to go.
Congrats on your new car, and welcome to the world of Model A's!