I started out wearing contacts, but I was losing them regularly and I didn't like having to close my eyes every time I got splashed in an effort to not lose contacts.
I switched to glasses and I have been wearing the same pair of glasses thru more than 9 years of paddling, 500 river days. The key is getting the right strap, along with shatter-proof lenses and tough, flexible frames.
I don't have to close my eyes when I get splashed, and I can open my eyes while under water, which I find useful.
The drawback is, if it is a humid day, you can have trouble with fogging.
Fortunately here in Colorado, that is rarely the case. The air is so dry, I only have fogging problems about one in 10 river days.
my 2 cents.