It doesn't leak at night as pads do, it's cheap and environmentally friendly, but mainly that it doesn't dry out my mucus membranes and doesn't contain bleach and pesticides that I don't want anywhere near my uterus.
I have only used it during one period so far and I'm sold! Don't need to think about it, so nice to go and do what one wants and to not constantly have to think about if you have tampons with you etc... I love my cup!
Congratulations on your 3 year anniversary! I recently started using a menstrual cup and the only thing that I'm sad about is that I didn't start with this sooner. It's amazingly great in every way!