Yah, there’s a lot to fins… flex, rake, material, placement… and there’s a terrifying trend lately to make the trailing edge super sharp, which is just crazy. SAND DOWN THE BACKS OF YOUR FINS! For most surfers, fin cuts are the most likely way to end a session early and badly – either by cutting you, your leash, or other surfers. It will make the board a tiny bit slower to sand the fins down a bit, but it will save you some swims and possibly a trip to the hospital. Sand those things down enough that you can hit them with delicate parts of your body without putting holes in it.
OK, next important fin difference is size. Small fins are faster and will slide out easier, while larger fins are slower and hold better – I like larger ones for a more drivy style. You also want fins that flex a bit, so when you’re making a turn they store some of the energy and then release it back, like bouncing on a diving board. Too little flex and it’s going to be unforgiving, too much and they’ll perform poorly during hard turns. Material – light and strong’s always good, and you also want to be able to sand little dings out of it, because dings on the leading edge especially will increase turbulence and drag. Plastic fins are OK but tend to break at the attachment points. The fin shape is going to make a difference too. Fatter fins are generally going to be more forgiving and perform well over widely ranging conditions, while narrow fins will be faster only in the sweet spot. Great things about fins these days is you can swap them out – try weird combos and see what you like.