I use MESS (UME actually which is a combo of MESS/MAME) for several reasons. First off, the scanline filter that is available for this emulator is hands down the best looking scanline effect that I have seen of all the emulators I've tried. I have a rather large LCD monitor in my "showcase" style cabinet, and the scanlines on most other emulators are too thick to look realistic. The second reason I prefer this emulator over others is the fact that I only have to update one emulator as opposed to trying to keep up with dozens. The third reason for using MESS is the fact that I can manipulate the screen size very easily. For handheld systems, I tend to shrink the screen size so that the games aren't so pixelated that they're unplayable. While it's true that MESS doesn't always emulate some systems as well as other system-specific emulators, it does emulate the more popular systems (NES, SNES, Genesis, TG-16, etc.) almost perfectly. And for the systems that have them available, the cheats are very easy to use. I highly recommend MESS if the features I've listed above are also important for ur setup.