A couple other options worth considering.
Norsso. Their slides are 17-4 stainless, so a bit nicer and theoretically more durable than typical 416R of most aftermarket slides. If it was me, I'd avoid all the cool guy unnecessary slide cut BS and stick to the Gripper or Spec Ops models since those are fairly conventional and Gen5-like with simply having front cocking serrations.
Remsport. Best bang for the buck by far ($140). It's 416R stainless, melonited, so pretty typical. They are very nicely machined and finished (much more so than the Brownells slides), like impressively so for the price. In fairness, I've heard a few people say they had some issues with them. I haven't had any issues across multiple slides. I do wonder if any issues people have had is due to the off-brand internals they might be using?
I stick to OEM
slide internals except for a few components where there are
quality aftermarket options (e.g. Overwatch Precision NP3'd OEM striker and firing pin safety, Apex extractor only if addressing extraction issues, White Sound H.R.E.D. for addressing weak extraction, etc). Regardless, I always stick to OEM for the striker channel sleeve, striker housing, striker spring, striker spring cups, end plate, firing pin safety spring, RSA. With those cheap and small parts, I have seen wide variations in specs and reliability issues from the sheer number of aftermarket options. So, I see no reason to deviate from OEM for those small components. Also, when in doubt, try an OEM barrel if assessing any issues before entirely writing off a slide that might have problems.
Both of the above have separate optic recoil bosses (preferred IMO) as opposed to the weaker design of raised screw hole bosses of many others on the market. As an aside, I wouldn't give SI a penny, but that's just me. Reasons why have been discussed ad nauseam elsewhere and don't need to pollute this thread but, suffice to say there are reasons.