I've worn glasses nearly my entire life (parents didn't know i needed them until the 1st grade). When i started playing paintball, glasses quickly became a burden - they don't fit well under most goggles & they fog easily without lens treatments. I switched to contacts exclusively for paintball. It was a very difficult transition, but damn worth it.
Upside - free to wear any paintball mask. Improved vision over glasses because a lens directly on the eye provides better results than a lens that hovers in front of your eye, plus you gain full peripheral vision as well. Contacts do not just pop out unless you rub your eye extensively (which you shouldn't do, regardless).
Downside - better hope to Crom you've got vision insurance. At least you won't need a lot; i've been using the same batch of contacts for over 2 yrs. Only wearing them one day a month at most, they last a super long time.
My personal downside/curse: i have purchased SOOO many sunglasses. Every summer, when i'm out & about more, i'll wear my contacts with more frequency. And every summer since getting contacts, i buy 1-3 new pairs of sunglasses.