Cigar ashtrays are unique because of their size and proportions; they are usually big enough to accomodate lots of ash and hold large ring gauge cigars at rest.  Cigar ashtrays come in many shapes and sizes so they can rest single cigars and/or multiples.  When choosing a cigar ashtray, any Tobacconist can tell you that one of the most important criteria to use in your selection process is the ease of cleaning - having a smooth and easy to clean surface is practical and important over the long term.   Also, keep in mind whether your ashtray will hold up to the elements if kept outdoors - attachments like anti-scratch pads on the bottom can get damaged in water or snow, while glass will hold up well outdoors.