Proper use of 申し訳....(details)?

Question:

I'm always confused by these phrases
Moushiwakearimasen (申し訳ありません）<-this one is polite, and most commonly used?
moushiwakemasen (申し訳ません<-is this one even grammatically correct to use???
or moushiwakegozaimasen (申し訳ございません）<-is this the one that's most polite?

I know what it means, I just can't seem to get when it is proper to use one or the other.

Answer:

I would use「申し訳ありません」
「申し訳ございません」should be more polite, but sounds too much or diplomatic (to me)