Having used ALS, SLS, and Combo ALS/SLS units, I prefer ALS, opposite of poster above. SLS causes the holster to ride higher, it requires the manual reactivation of the locking mechanism, it's slower, and while the combo unit gets rid of the necessity of manual relocking, ALS gets rid of all the negatives with no drawbacks, plus you can get red dot capable ALS holsters, but not SLS. I have run and own examples of all of them.
I run only Safariland holsters when possible but run 2" drop plates from both G-code and Safariland. Without a leg strap they both can move when running, both can get torqued on draw, but are the best option for a non drop leg. The best drop leg is the Safariland 6004-10, single leg strap, with rubbery drop flex adapter . G-code lacks extra mounting points on their single strap, high ride, leg rig and lack the rubber drop flex afapter that Safariland offers, opting for nylon only, so Safariland is less prone to moving on a draw.