MPlayer was part of a company that is now focusing on making voice recognition products, and with the elimination of their multiplayer service, can dedicate their resources more fully to their products. GSA bought out MPlayer, and the company that runs MPlayer is dedicating themselves to making other products. Both MPlayer and GSA have pros and cons. I'll list them here in no particular order. Simplicity of use.
Popularity makes it easy to find opponents during the whole day.
Pager feature is more versatile. Really eats up a CPU's resources and modem speed. Overcrowded at peaks of service use. People tend to be less supervised. Porn addled at times.