I've used the Keeper and the Diva. They're both much of a muchness, though i find both a little long and trim the extraction stem right off at the bottom of the cup so it can't stick into me. I have seen photos on the internet of all 3 next to one another and i think (might be best to check) that the mooncup is the most petite in length - they all have similar rim diameters.

Personally if i am asked i advise women to buy a silicon cup (moon or diva) simply because after 3 years of use i developed a rubber allergy from the keeper. That won't happen with everyone, but it CAN'T happen with the medical-grade silicon products.

Bx