ALS is the Safariland thumb-button which moves a plastic retainer which clicks into the ejection port. It's only a Level 1/2 if you count the normal tension screw. SLS has the U-shaped hood which you depress with your thumb and rotate forward. They have some Level 3+ holsters which combine both I believe.
The SLS is a bit more secure I think for duty use. It's harder for a perp to grab the hood, push it down, and rotate it forward --- whereas the ALS is just a button to depress while pulling.
The Blade-Tech WRS system is tits. I ran it for about two years in the patrol when they let us use qualified holsters. The WRS is a metal U-shaped hood, much like the SLS. However, with the WRS, the hood is spring-mounted. You hit the lever inward toward your body (same exact muscle memory as the SLS, with much less movement) and the hood automatically shoots forward, allowing a draw. It basically takes a step out of the SLS style movement.
I think the WRS would be equally as fast as the ALS model from Safariland. I trust Safariland more when it comes to retention in a fight or someone trying to grab your gun. They just use stronger plastics/materials than just about anyone else. I was not a huge fan of the Tek-Lok system I had on my Blade-Tech holster. It never failed me, it just didn't inspire the same confidence as the 2" belt loop on the Safariland.
Do you have a "Level" you're trying to meet. All of the options I've mentioned are more or less Level 2. There is also something called an ALS guard, which is a sliding cover to the ALS button. You slide the cover forward, depress the ALS and draw. There are a ton of combos with the Safariland --- not sure how many work with the PPQ.
My Safariland is about 20+ days out (CopQuest has to order them from the factory), so it'll be a bit, but I'll do a review on them. I may call Blade-Tech and plead for a light-compatible WRS holster.