Well, I'm sad to report that after at least 9 months of struggling with three different cups (Diva, small Lady Cup and large Lady Cup), I'm going back to tampons :(. Yes, they're not the most comfortable things, but I'm tired of going out clubbing and having to wear a back up pad to catch the inevitable leak and I'm tired of my bathroom/pants/hands/panties looking like the site of a massacre. I've been on this community for months, and as an experienced cup user, I know I'm getting a seal, I know I'm inserting it properly, and I don't think it's a sizing issue- I had the most luck by far with the small Lady Cup. It just seems that my anatomy is not suited to a cup. I have a tilted uterus and my cervix is always far off to the left, which means that no matter what I do, blood always gets past the cup once I've been wearing it for a while. I never had trouble with tampons, and I think I just need to do what works.
This community has been really helpful and I wish everyone luck! I wanted to post so that others who do not have success with their cups know that they're not alone. :)