[IATW]

Another vote for the Brownell's optics-cut slides.
I have a G19.4 with one and it's been flawless. I ran 1,000 rounds through it before using it as a carry gun, with zero issues and no problems with optics mounting.

The only things I'd change about it are the top cut-out and the forward slide serrations. The cu-out hasn't offered any tangible benefits, but does trap lint, etc. I don't like forward serrations at all. They're just another abrasive surface and I was taught malfunction clearances that did NOT involve putting my hand/fingers near the muzzle of a gun.

 

[spadedracer]

I've had Zev, Agency, a single BEC, and recently picked up a LWS slide.

No issues with any of them, and the LWS appears to be a mill job on a OEM slide with some beautiful machining and finishing work.