The MUM used to be the worst magazine in Magic. Moehring took over and made it an excellent resource. Now Mike Close is in charge and while I have only seen a couple of the issues he has produced, I have faith he his delivering the absolute most he can with the budget he has to work with.
I don't know if you are required to join an assembly, however there used to be a clause which said you would if there was one nearby. Of course, this type of thing is never enforced. However, if you do move around a lot, being a member will allow you to attend any assembly meetings. Some clubs have Draconian rules about guests.
Both Magic and Genii are excellent resources. They have different slants and feels. Some people love one and not the other, but most people subscribe to both.
They both have tricks, reviews, articles about current events, and explorations of magic ideas and persons of interest.
I cannot currently recommend the Link Ring magazine. It has really gone downhill and I rarely am able to find anything of any interest or depth in it's pages.