Is the Glock 43X or SIG P365 better for carry?

Both are excellent; it is about fit and feel. The P365 packs more capacity in a slightly smaller package and has a crisp trigger; the 43X has the Glock ecosystem, a slightly taller grip many find more comfortable, and legendary parts/holster support. Handle both — whichever points naturally and lets your hand get high on the grip is your answer. You genuinely cannot lose here.