I used MapTool for my D&D 4E Dark Sun campaign. I like that incredible flexibility the program offers, being able to tailor it to my exactl needs, making encounters, maps, enemies and everything just as I want without habing to compromise on the presentation. I generally like to tinker with stuff and am never satisfied with the "vanilla" version of anything, so it's a big plus, and it helps that I am fairly skilled in Photoshop to create my own tokens and environments. Otherwise I would may prefer something simpler with less choices but more user friendliness.