I don't have the Mona but one I do want to use, but I have the Gigi and by far it is my favorite G spot vibe. The various patterns and adjustable speeds gets me off every time.
I do not own a Mona, but I own an Ina and a Gigi, and I far prefer the shape and curve of of the Ina (which is the same as the Mona's). It's probably a matter of personal preference though.