Both. You should have a recessed lip directly above the monitor where a small piece of tinted grey glass rests flush with the tabletop. Then the top piece which covers the entire tabletop should be clear and tempered.
why not just have one piece of tinted, tempered glass?
because if you have a graphic underlay it will be hard to see, but the gray make the game images look great. Thats why using two separate pieces is nice
Right. The artwork is very hard to see underneath the grey tinted glass. Also, for aesthetic reasons, I think the clear glass looks much nicer on top, especially on each end where it is not resting on anything (above the CPs). Plus, the grey glass directly above the monitor really hides the screen when it is not in use if you have a black bezel.