Fins themselves come in two traditional blade styles: a split or paddle blade. Both styles have pros and cons to them with distinct characteristics. A split blade is a more novice blade for a snorkeler in a sense. These fins allow water to pass through the split in the blade on your upward fin stroke, causing less resistance and more propulsion. This compensates for incorrect kicking techniques which make split blade fins ideal for beginners; you won’t waste all your energy and attention on kicking and can instead enjoy looking at colorful marine life. Bottom line is you get excellent propulsion with the least amount of effort with split blade fins; it is because of this that most novice snorkelers prefer them.
The other main style of fin is the paddle blade. These fins do not have a slit down the blade like the split blades styles. The advantage of this design is it allows for more drag against the water when you kick which results in more powerful propulsion forward. Paddle fins are ideal for avid snorkelers who have their kicking technique down or for those who will be snorkeling in or against any currents. If you are a beginner snorkeler and do not have the best kicking technique, the paddle fins could cause cramping due to the drag they present. However, if you are snorkeling in an area with any sort of current, you will absolutely want paddle fins. While the split fins offer ease and comfort, their split blade is ineffective in propelling you forward against a current easily. If you have paddle fins, the drag they create will move you forward in a current with ease.
All in all the type of fin you decide to get should come down to what type of snorkeling you intend on doing. If you are looking for easy, effortless kicking then split blades are for you; on the other hand, if you intend on snorkeling in more lively waters, paddle fins will give you the necessary power to swim all along currents easily. If making a decision becomes too hard, buy both!