Side mount is the easiest. Anyone who has the slightest idea how to gunsmith on AKs and has the rivet tool can install one in minutes. It is tall, but reliable, the mount rail isn't too obtrusive if you do not want it later, many options for what to clip to it, including mounts integral to the scope/RDS (if you go Russian) to keep the mass/height/snag down.
None of these photos are mine
Receiver cover rails will wobble, flex etc. None suggested as far as I know. I have no experience, no reports, but a few are making receiver cover replacements like this
https://loadoutroom.com/thearmsguide/watch-texas-weapons-systems-dog-leg-ak-cover/ that mount it rigidly somehow or other.
I know a number of folks very happy with the Ultimak. Clever RDS selection gets you to co-witness, so I hear. Yes, gets hot so plan accordingly. Don't touch the aluminum above the lower handguard.
A few similar front rails also exist; Zenit for example makes some used by the Russian military / security services, but as much as I know Zenit electro-optics are fine, I know no one personally who is using any of the rails so have no further data. They do have US distributors.