Make a list of desirable attributes such as manufacturer's accuracy history, power level, magazine feed or single load, semi auto, overall length, loaded weight, style, State laws regarding use and power levels, etc. Look around forum for negative feedback and "required" upgrades and "fixes" to certain manufacturer's. With a narrowed list, don't forget to look at YouTube videos to see how each stack up too. Also on that list, that most don't think too much about until the rabbit hole happens is "buy once, cry once."
The newest 45 to the show is the semi auto Western Rattler 45 and Rattler Long Strike. The Rattler 45 has been getting good reviews, and very little issues with the semi-auto function in any Rattler caliber. I put another 50+ slugs through mine tonight. My Rattler Long Strike is a consistent 2 moa shooter at 405-420 pfe. The twist rate likes a decent weight and longer length of slug.