Here's my experience (for what it's worth).
I've owned a pre-ban 14.5" AR, a post-ban 20" AR with gas check, and an IMI M1 Carbine.
My son (who was 9 at the time) did not like the 14.5" AR because he said it "kicked too much". It was light, and had the little CAR stock on it which has less surface area and is fairly uncomfortable anyway. He LOVED the M1 carbine, and I too felt that it had no recoil, and a moderate muzzle rise. The 20" AR was his favorite by far (until I got the Storm
) because he said it had "no kick at all" and because of the brake, it also had no muzzle rise.
BUT, for me, standing next to him while firing that 20", it hurt like
because of the blast. You felt it, not just heard it.
Of the three, I'd say with FELT recoil, the 14.5" (and 16") AR's have the most "felt" recoil, M1 carbine next, and the heavier, longer barrelled 20" AR has the least. Probably does have a lot to do with barrel length and muzzle blast directed at the shooter though.