To some extent, there's a trade-off between fast and comfortable. More specifically, a bike with front suspension and fatter tires will most certainly be more comfortable (smooths out the bumps), but it will take noticeably more effort to ride at a given speed than a bike with no suspension and skinnier tires. At higher speeds, wind resistance becomes the limiting factor, so a road racing bike that gets your upper body down low (generally considered less comfortable by beginning riders) has the advantage...but I don't expect this will be as much an issue for the average commuter.
All this is to say that this speed-comfort trade-off is something you might consider when shopping around. As for "easy to ride", pay attention to shifter style, if you care...e.g., grip vs. trigger shifters.
My guess is that a Trek FX series bike or something similar would work well for you, as nadom suggested. Consider posting on the commuting board for more advice...
Meanwhile, remember to budget for accessories and other items handy to have for commuting, e.g., mini-pump, patch kit, maybe rack and fenders, pannier if you want to carry stuff on the bike, lights, etc.
A bit off topic, but road bikes are not really more suceptible to punctures. Your choice of tires is probably a much bigger factor, even for a given tire width; there are well-armored tires and poorly armored tires, whether on a mountain, hybrid, or road bike...