Cups, in order of ownership/use.
(1) 2000: The Keeper, both sizes. This was 10 years ago, when The Keeper company was the only cup company around, at least that I knew about. I fell in love with the concept of the cup, although I wasn't fond of the Keeper itself. It was uncomfortable and I found cutting the stem, even all the way down, made it worse. I bought another one, the larger size since the smaller one leaked, and vowed to never cut the stem of cups again. The larger size did help with leaking. I developed an allergy to latex after using the Keeper for a couple of years, so I went back to tampons for a year or so until...
(2) 2004 or so: Diva: I was thrilled to find a menstrual cup made of silicone. I could return to menstrual cups again! My experience with the Diva was not pleasant, but it was still better than tampons and since I had no allergy to it, I could use it. Unfortunately, the stem was very pokey and uncomfortable, and the irritation usually resulted in a yeast infection following my period. After what happened with cutting the Keeper's stem though I refused to cut the Diva's stem. Additionally, the suction was unbelievable, and very uncomfortable, not to mention painful for removal. I got both sizes, and found the larger one resulted in less leaks, as with the Keeper. I was disappointed, and used the Diva off and on for 4 years, alternating with tampons because of this discomfort, until...
(3) 2007: Lunette (the larger size. They didn't have the smaller size out yet when I bought mine.) Why didn't I buy the Lunette sooner?! It was WORLDS better than the Diva! Not only did it fit much better because it wasn't so long, it leaked way, way less and was far more comfortable thanks to the flat stem. It still poked a little, but not nearly as bad as the others. The suction was also far less powerful, and it was just a better designed cup all around. I vowed that I would only buy flat stemmed cups from that point on. However, the Lunette was a LITTLE big in a way that it constantly made me feel "full" or like I needed to pee, only when I tried to pee, it seemed my "pee tube" was squished and it was difficult to pee. Also, when needing to poo, with all cups I found that they got in the way of pooping comfortable so I had to remove them before and put them back in afterwards, but the Lunette was especially bad with this. Even though it leaked far less than the Diva, I still always had pink toilet paper when I peed and very, very light spotting on my underwear. I chalked this up as being normal and nothing to really be concerned about.
(4) 2009: Mooncup UK: I'd felt drawn to the Mooncup UK since before I found the Lunette. But I never got it because it was so widely known to be small, even the larger size, and not hold much. I'm a heavy bleeder, so I figured it would not work for me based on capacity. But starting around September or so of 2008, my Lunette began refusing to go all the way in, and began to easily get pushed out. I discovered it was because my cervix was riding lower during my period than it ever had, and by January of 2009 I realized that it wasn't going to return to it's previous state. So I decided to get a Mooncup to try, because I was not about to give up cups. I got the larger size, for obvious reasons. When I tried it for my first cycle, I left the stem intact, and it present the same problem with discomfort as did the Diva and Keeper. It wasn't going to work because of the stem, but I noticed that was the only way it was uncomfortable... I couldn't feel it inside at all, and could pee AND poop comfortably without removing it! I also noticed it had no leaks at all - not even a pink tinge! So I decided I had nothing to lose and cut the stem down until eventually it was completely gone. Not even a ltitle nub... it's almost concave where the stem used to be (once I file down the edges it will be perfectly smooth probably). The first day I wore it with the stem completely gone, I heard angels sing. I can't even tell I have it in. I can pee and poop with it in just fine. And NO leaks. AT ALL. It's like I don't even have my period. Maybe this is just a freakishly lucky cycle with my period, but I'm staying with positive thinking that I have just finally found the cup for me. It makes me really sad that MooncupUK decided to stop shipping to the US just when I discover that this is my cup, and I hope that when it comes time to replace it, it isn't going to be difficult to obtain another one. For this reason, I disrespect The Keeper company even more than I did before.
Hope this helps someone!
Edit: Forgot to add info that might help. I am 29, and have never been pregnant or had children. In 2000 I was 20, and since I was 29 when the Lunette stopped going all the way in half the time, it probably has to do with body changes around 30. So when you hit 30 or so, it may not even be a size issue with cups but merely the shape or even the holes, etc.