I have a VERY old Delta professional 10" miter saw, not a slider though. Very well made tool and has worked flawlessly for all these years. I also have two DeWalt 12" slider miter saws, one with the light that casts a shadow where the blade will cut and one without the light. I rarely use the Delta miter saw, but on occasion I do use it for cutting scrap pieces of wood into smaller pieces so I can more easily get rid of them.
I don't always need a 12" miter saw to cut the wood I need to cut, but having the 12" miter saw makes more sense to me than having a 10" miter saw. What I mean is, with the 12" miter saw I am pretty well set to cut most anything I need to cut whereas the 10" inch miter saw may not be big enough in some cases. I just figure if you are going to spend some money and buy a miter saw, buy the 12" saw and then you are all set for pretty much anything you need to cut. If you buy the 10" saw you may very well, at some point in time, wish you had purchased the 12" saw instead. In other words, you can use the 12" saw to cut small pieces of wood but it is difficult to use the 10" saw to cut real large pieces.