The SA on your lower quality GK will effectively give him an extra star when an opponent's ST gets one on one with him to shoot at goal, so in effect they'll both be about the same in that situation, although in normal situations your higher Q keeper will be better.

I'd rotate them both, and let them both play games, as eventually the keeper with the SA will overtake the other keeper in quality, as he's younger and will train faster, then it's simple which one you'll want in the end