This is just one man's opinion, but I think that anyone who swims in the ocean, much at all, should consider getting their own mask, fins and snorkel. Rental equipment, anywhere, can be kinda lame. In the long run, for most folks, it's gonna be cheaper to buy, too. And too, that way, your stuff is always ready for you when you want to go swimming, no worries about getting anything back to the shop.
Fins for snorkeling should have medium size or even small size blades. I like ones with seperate booties for snorkeling especially as you can pull off the blades and still have shoes on, which is a real good thing as there is stuff that will sting you or cut your foot, especially if you put your weight on something. Urchins come to mind right off.
I have one set of fins for scuba with large blades and one set with much smaller blades for snorkeling, and I find it much to my advantage.
Course, what works for folks is what works. I don't think there is any one right way.