The later Beselers, after the original 45M, can align the negative stage to the base easily with the supplied hardware, which allows back and forth and side to side motion of the whole focusing rail. You need an adjustable lens stage to finish the job. Zone VI and Delta both make (made) one in Leica thread size. However, making your own for any size does not take machine shop expertise. (Briefly) Take two Beseler lensboards that hold your lens and clamp together. Drill three holes 120 degrees apart of tapping diameter for three machine screws or allen screws around the hole. Tap three holes on one board and re-drill screw clearance holes on the second board and assemble a sandwich with the board with clearance holes board holding the enlarger lens and the filling of the sandwich a piece of dense foam with an appropriate circular cutout, and screw the two together. When mounted on the 45 you can now easily align the lens stage to negative stage and base of the enlarger with a screwdriver. If you are using a glass negative holder you can align in seconds for any print with the Versalab laser thingy. Unfortunately, for the Beseler 45, you will find that you have to do this almost every time you change the negative height! (i.e., you can nitpick if you want to - for 4x5 this probably will not improve quality as much as you hope. Alternatively, by obsessively aligning you can shift blame of any technical shortcomings of your prints to some other cause.) If you are using Cold light or a color head and you are somewhat handy, you can remove the upper bellows and use 1/4 inch plywood to make a box to hold the head, which screwed upon the upper negative stage will make the upper assembly more rigid.

As regards the Saunders, you can shim the column to square it to the baseboard as measured with Versalab bouncing off a glass negative holder. Unlike the Beseler, this fix will probably work well for a range of heights, but make sure your baseboard is as level as you can get it before playing this game. The lens stage is "factory aligned", which means that, by the time you can get one you can afford, it is not likely to be very well aligned. Nonetheless, on the later models, the fixture that holds the lensboard can be removed and shimmed and quite likely an adjustable lensboard holder could be fabricated, although I have not tried this. The various rollers that hold the head in place on the column have to be clean and in good adjustment (they are adjustable) for this to work at all.

Summary: Beseler easy to adjust but seems to need it constantly; Saunders maintains reasonably constant alignment after some fairly tricky and time consuming fiddling. This is my experience based on owning one of each.