Mobile Me, You, and Them?

I am a babe in the woods with Mac, just two days old. I want to know about mail. I have MobileMe, so I have access to MobileMe mail, BetaMobileMe mail, and the default mail program on my dock. Is there an advantage of one over the other? Also, my primary mail account for many moons has been with Comcast. Is there any advantage in switching to my .me mail account, or is it possible to merge my Comcast one into the mail one so I can use the two together as I do on my iPad? Yes, to my knowledge, the only way a newbie can turn into an oldbie, is asking questions. Thanks in advance for your replies, in spite of the potential lack of insight on my part.