I had the same questions when I first started out in NRA Hunter Pistol. Here are some things to consider: Availability of a barrel, RECOIL, cost of loading, what can you get by with.
There are lots of good choices but sometimes the barrel is just not available to buy.
I put RECOIL in caps because that is what I found out to be the big problem with the bigger cals. It may not bother you to shoot a 357 mag when you are just shooting at cans but when the buzzer goes off and you are concentrating on getting the shot off, the last thing you need is a thump when you do, especially when you have already been thumped 30 times. That 30 carbine may be a good one to load down and it may be a good cast bullet canidate.
The cost of shooting may not seem like a big problem but if you are going to shoot good, you have to practice and you will practice more if you can get good ammo cheap. There are lots of people who get a AAA rating with the rimfire and consistently shoot AA with the hunter pistol. Most will say they practice less with the hunter pistol equipment.
I have a friend who got his master rating in hunter pistol last summer. He has always shot it with his 22 rimfire barrel. He uses Aguila 60gr ammo for the pigs and rams. I used my rimfire barrel for several years until I made a decision on what I wanted to shoot. I borrowed several barrels and ended up getting a 22 Hornet. I like because I can load it down for silhouettes and then load it up and go out and bust whistle pigs or coyotes in the off season.
Look hard at what the other guys are using. Especially the ones that are consistently winning.
One important thing is to use what you have until you can decide what you really want.
sixgun