Much of what dervish says is pretty agreeable.
I prefer advanced mainly since I find the slow pace a good thing; an irony with forum RPs I've noticed is the more "advanced" they get, the less time you actually need to spend roleplaying which is good for me since I need the time to study or improve on other skills like drawing or coding.
You only need to post once or twice a week, as opposed to casual RPs where you should post once or twice a day. Or like in free RPs where you need to post multiple times a hour or else like in the OP's case, completely fall out of the loop.