What Crankin said--what is most important is your gear ratios, and you can now get as wide a range with a compact double as with a triple. A reason to go with a triple over a double would be that with the double a wide range will mean a little bigger jump between gears than the same range in a triple. Sheldon Brown's gear ratio calculator might be useful--you can plug in the info for what you have with your triple, and see what would produce the same ratios with a double. http://sheldonbrown.com/gears/