Video Lagging, PLEASE HELP- format?

Okay, so i've made a video off of sony vegas ( the trial version ). I watch it in the program, and it is fine, it does not lag or anything. Then i've rendered it as WMA , and M2T, and it doesnt work well. I watch it, it lags, enough so that the music is out of sync. But then i render it as MPG and it works fine, no lagging, but the quality is not very good. Is there a reason why it does this? because i still want the quality to be good without it lagging! thanks!! )