RS Regulate makes hands down the best side rail mount in the industry. I've heard good things about AK Master Mount via AKOU as well. Both these mounts have several optic attachment options which can allow you to get a very low profile mount. I have a 2nd Generation Midwest mount which has held zero very well, but the Yugo model has fewer optic attachment options so I have a higher profile mount than I would like. For Yugo rifles I'd recommend RS Regulate or Master Mount. Master Mount also sells a side rail that can be retrofitted to rifles that do not have a side rail. Rob Ski of AKOU has apparently had good luck with this option on his Beryl.
I have a TWS Dogleg rail on my Beryl (it also lacks a side rail). I have been extremely happy with it so far. I've noted no shift in zero and it is solidly built. While it hasn't been in the trenches of Avdikka with me, I have run it fairly hard. I do worry about how resistant to zero shift it would be to a drop, but honestly I would have the same worries with an Ultimak or side mount for that matter. Then 2nd Gen TWS allows you to remove the entire dust cover when performing maintenance on the rifle eliminating the worry of it being damaged if dropped during cleaning. The TWS gives the lowest possible profile mounting option. It is interesting to note that it is not uncommon to see Russian "Alpha Types" with what appears to be TWS dust covers on their rifle and that the Ukrainians are manufacturing and selling what appears to be a direct c
opy of the 1st gen TWS rail.
The chassis rails such as the one 4RN has shown are a popular option as well, but I don't have any experience with them. I have thought about trying out a SureShot USA rail as SureShot is of Russian origin and domestically gives Zenitco a run for its money. The Midwest Industries chassis seems to be inspired heavily by the Zenitco rails and I've heard they are solid. Price (looking at $300+), compatibility issues with my Beryl and Yugo pattern rifles, and the added weight have prevented me from anything more than daydreaming. Ukrainian chassis rails are also being sold by AOA and may be worth a look. I'll also note that some of these systems with the cantilever optic mounts that extend over the dust cover appear to give a higher profile mounting than I would like.