If I had a pro shop I would get a manufacturer dealership to get the best price, and stock those strings.
Most home stringers cannot get those great deals.
Years ago, late 1960's, I had a dealership with Bancroft Sporting goods and string prices were very much reduced. Now most need store front shop for decent dealer prices. Since you have a shop, I would go with whoever you can get the best deal with. Most manuf. have similar synthetic guts, multi strings and similar poly strings be it soft or stiffer hit poly strings.
Only thing is if you are changing your current inventory of strings as you say, many players at least for me , ask for same strings as last string job,like I have customers that like X-1, or RPM Blast and ask for it specifically and strung same as previous times, and if you change inventory how will that go over? If you string RPM Blast for a player for last couple years and now you change inventory, are you going to This is why I carry what players typically hit with in my area. Many of the strings I carry I would not hit with, but many of the people I string for like them, so that is what I keep in inventory. There is a group of hitters that have no idea of strings or preferences, and when I find that they hit with a typical syn. gut I go to PSGD as that has been one of the most popular strings used in pro shops for over a decade. In reality most any syn. gut would do for that type player.I would not hit with that string, but you have to go with what your customers may want, and that could be a big difference.My string is all nat. gut, and I do string a lot of nat. gut jobs, but I do not push that string just because I use it and like it. It is not for everyone and also $ wise.
It seems to me , once you start stringing for players, over time you get a feel for what the players in your area or your shop customers want and you end up ordering those strings for your inventory, and in reality no one else can tell you what to stock, and only advise as to their favorite string is all.