as mentioned above, measuring your sit bones is key to getting a saddle of appropriate width. as far as shape, cut out vs. no cut out, nose shape, etc. it is just a trial and error thing. some shops will let you try a demo for a while, but you really need some time on the saddle (and some longer rides 3-4 hours) to know how well a saddle agrees with your backside.

specialized has the ass-o-meter to measure sit bones, or you can google it and find some at-home methods.