The first AR I built up was a 20" with a CAR stock, and frankly I thought it balanced poorly compared to the standard stock. It had a heavy barrel, so that might have been (probably was) the main issue, but it never looked quite "right" either, balance aside.
The next one I assembled was a heavy barrel carbine with a full size stock. Nice to use, nicely balanced.
My third AR was an M4orgery, and it was nicely balanced as well.
My current AR has a 18" SPR mid-length barrel with an ACE stock, and I am mighty pleased with it. For me, it is the best of all.
I suppose a standard weight 20" barrel with a CAR stock
might feel OK, but it is, after all, a matter of YOUR personal taste. Besides, it is not as though you can't change the darn thing out iffen y'all don't fall in love and get married!