> What leveling scheme should I use and what is the best stable version of Marlin for this?

It depends on what your need. The various bed leveling schemes all offer different advantages. The UBL (Unified Bed Leveling) branch is trying to bring the best of all the different techniques to all printer types. It is trying to make it so you don't have to pick and choose. Right now, it still doesn't work on Delta printers but that is its primary focus. It will work there soon enough. That is what it was designed to help. And so far, it doesn't do the Grid Based Leveling with a Least Squares fit on the sampled points. It will do that soon enough also, but the truth is, it isn't even needed.

Seriously... I went to to the Dollar store and got the worst piece of glass I could find. I found a picture frame and when I held it up to the light I started giggling. I got a piece of glass that has huge ups and downs on it. And one side is thicker than the other side.

But here is the important part: I can get a perfect first layer across the entire piece of glass every time. It doesn't matter where I put the part, or how it stretches across the glass. I get perfect adhesion on the first layer every time. And that piece of glass I'm printing on sucks!