I don't think that sliders are worth it. I have a bosch glide and there is a lot more play in the mechanism then they give it credit for. All of my critical cross cuts are done on the table saw with a $150 miter gauge and the accuracy and capacity is FAR FAR greater than any miter saw could achieve let alone a $150 miter saw. if all you need is 90 degree cuts a homemade sled can be extremely accurate and is incredibly cheap. I made one from free material i got from old cabinets or other various places.
If you must get a miter saw, i like having one that uses the same sized blades as my table saw. It allows me to use blades between the two of them. I'll have a junk blade that i put on each of them if i need to cut questionable material that may or may not contain dirt, metal, or other material that may damage a saw blade.
Another cross cutting mechanism that has more value is a track saw with a good blade in it. Using an accurate square with the track i can get good accurate cuts for as long as i have track. With large heavy items taking the tool to the work is a lot safer and also can be more accurate.