I've got the vortex lo-pro, the original vortex one, Spuhr mount with bubble, MK machining 3d printed, and Accuracy 1st scope levels.
Vortex lo-pro is great for being light and low profile but is a bit of a **** to get setup perfect because it rotates slightly as it is tightened down. Original vortex one works fine but is heavier, higher profile, and catches on stuff more than the lo pro. Accuracy 1st levels are just damn nice but a little heavier.
Anything in line with the bottom or top of a scope I.E. built into spuhr, picatinny, or top of the rings is not ideal from my experience as you usually have to move your head to see them. A level on top of a scope ring can impair your vision of your elevation turret. With something offset to the weak side of the scope you can look at it with your off eye without moving your head. That pic mount level posted by XLR looks like a nice option. I do find it convenient to have it mounted to the scope if you ever move scopes between rifles.