Milling my Glock 19 for an optic, which one do y’all recommend?

They will fit the same footprint.

If your holster will support it Id recommend the SRO. Top load battery, larger window, dot definitely appears a bit more crisp to me, have had several of each on different platforms. Work gun wears an issued RMR which works fine too.

Don't rule out enclosed emitter optics, definitely some benefits there and the 509T offers alot for the money.

I had an RMR on my MR920 and I loved every bit of it until I got my DVC Omni and bought an SRO. Night and day between the two. SRO for me from now on.

I like the size of an rmr

This is the key.

For a dedicated carry gun: RMR
Range gun/occasional carry gun: SRO

The sro has proven more delicate... If I were putting together a competition style pistol SRO would get the higher preference, but for a carry gun or something to take to class and run hard, rmr.

Whatever you can run an ACRO or Holosun EPS

I run a Holosun SCS-MOS on 2 pistols and like them a lot. One is on a G23 and the other on my G40 in 10mm. It's a solar charging unit, and turns on with movement. I haven't adopted the G23 into my daily carry yet. I wanted to put more rounds down range before going straight to that set up. But it's done well at the range so far. They are easy to dial in.

https://holosun.com/products/reflex-sight/scs/scs-mos.html

another option is the Ameriglo, RMR compatible. Trijicon bought Ameriglo a few years ago and designed the sight.

https://tacticalgunreview.com/walther-pdp-suppressor-red-dot-project/