Size depends on a lot of factors such as how much space you have for storage, etc. If you plan on buying instead of making your own, make sure that the insert plate can be easily leveled with the top. I know that sounds pretty basic, but I've seen some commercial tops that are horrible (not mentioning any brand names). Also, look for ease of adjustability of the fence system and be sure it can lock down firmly. Beyond that, there are a lot of features offered by a lot of different companies, some of which you may or may not want.