Assuming you're thinking about the incoming LC carbines? Depends on what you're gonna use it for. A 10mm carbine with hot hard cast/bonded loads would likely be a decent enough piece if you're tramping about in bear country. On the other hand, a .45 carbine doesn't really do anything better than a 9mm to justify it's cost/weight/mag availability penalty (.45 lc carbine comes in at the roughly the same weight as the 10mm, 7.1 lbs. Meanwhile the 5.7 one is 5.9 lbs and a PC Backpacker weighs in at 6.2 lbs.) Where I think a .45 would really shine is as a suppressor host, as .45 loads are usually subsonic (unfortunately a moot point for us). So if you're not already invested in .45, I'd go 10mm. Similar weight in a blowback platform, more power, and the only downside is more expensive training ammo.