I spent 2 days going back and forth on either Small or Large Si-Bell and eventually decided that I won't satisfy my curiosity, until I try both anyway and by ordering both at once at least I don't have to pay twice for shipping (which is almost half the price of the cup, so definitely a consideration). Small is nearly identical to a medium MeLuna in dimensions and capacity, so would be a safer bet. But I hear larger cups are often better for a "dangly" cervix and I like the idea of emptying it less often.
I considered Fleurcup too. It's very similar to Si-Bell in shape and softness and it would cost me half of what Si-Bell order totaled to, but for some reason I'm really drawn to Si-Bell's design and from what I gather Si-Bell's quality is better.
The bottom line is, I just ended up spending more money on cups than what a 3 year supply of disposable pads would cost me. And I don't regret it one bit! :D