I feel this needs to be bunched together as not all fins require boots.
Open heel vs closed heel fins
Personally I prefer to have open heel fins. Closed heel fins I generally associate with snorkelling. My issue with closed heel fins are that they just aren’t adaptable to as many situations. If you plan on cold water diving they are strictly off the table (a fact I learned the hard way as a novice diver on a dive trip).
If you ever have to make a shore entry over sharp rocks that lack of boots is going to cause you to think “I wish I had boots on”. Which leads to the question of which booties are best for me. The fit is the main thing. Just like any pair of shoes you own, if they don’t fit right you won’t want to wear them for long. There is also the consideration of high or low cut. Personally I like the high cut and I find that they generally last longer as the fin strap doesn’t tend to shift around as much. The downside is that you will generally need a zipper with high cut and that is a feature that can break. I would also try to find a pair that has a decent enough sole to protect from those pesky sharp rocks and insulate from hot sand. It’s also not a bad idea to look for rubberized sections on the back of the ankle and around the toes/upper foot. Big toes sticking out of worn out neoprene is an all too common sight. The thickness of the neoprene is also to be considered. As you increase millimetres of thickness it will affect your buoyancy. If you will be doing primarily warm water diving you don’t need as thick a boot, unless you want your feet to be more buoyant. This is also related to the type of fin you have (more on that in a bit). At the end of the day you don’t need to worry too much about which boots you buy, they are not going to last near as long as some of your other gear. They are basically a disposable item, luckily they are not a big ticket item. Get both a left and a right though, that’s important.
Straps vs. buckles
Aside from open or closed heel there are some other aspects to consider when buying fins. Something that is usually overlooked is the straps and buckles. It may seem like a minor detail, but they are the only moving part of the fin (or should be). The ease of donning and removing fins usually comes down to the configuration of the straps. If you are bouncing up and down off the end of a ladder on a rough day, you will want to be able to get your fin off and climb back on the boat with the least amount of hassle. It should feel natural and intuitive to navigate the catch on the buckle. Also once you do undo the buckle the last thing you want is to hand the fin up to the boat crew and notice that half the buckle has slipped off and is sinking back to the bottom. I’ve had to chase more than a few of my students runaway fin straps/buckles. For this reason more than any other I would actually recommend some form of spring strap. The logic being that if there is nothing to undo there is nothing to lose, simply pull it off the heel and that’s it. Of course the downside is that you lose the ability to adjust the fit that you have with more traditional rubber straps. Spring straps do come in different sizes though so that can be managed. If you do go for a more traditional rubber strap, it’s a good idea to have an extra one in your gear bag. Not the whole buckle assembly, just an extra rubber strap as they do tend to wear out over time.
What about the actual fin?
Now this is where it gets trickier, a lot of this will simply come down to preference. If you like split fins (personally I can’t stand them), then who am I to try and tell you different. Basically speaking there are only a few fundamental type of fins, split fins and a more traditional blade fin. Of course there are some others like force fins (which will also be useful on Halloween if you want to dress up like Donald Duck), but proponents of these type of fins will be the first to tell you why they are the best. I wouldn’t want to take that away from them.
Of the numerous options out there it can be hard to know where to start. One often overlooked aspect is the actual buoyancy of a fin. Does it sink or float or is it neutral? More importantly what do you want it to do? Do you have super buoyant legs or boots and want something to bring them down? Or do you feel like your feet are always dropping down and pulling you out of trim. There is really no single answer for which is better. I prefer a heavier fin but not something as heavy as Jet Fins. Again, this is where actually trying out gear on a dive will point you in the right direction the best.
When it comes to fin construction I am a big fan of simple over complex. The more different types of material used the more I feel it creates failure points. Generally it is where one type of material is attached to another that you see fins literally coming apart. A rubber(to keep it simple I’m using the word “rubber” but I know it’s not technically correct , each manufacturer has a fancy sounding term for the material they use) fin that is poured in a single mould quite simply has less chance of that happening. The upside to having different materials (at least according to the manufacturers) is that these different materials allow the fin to be “incredibly reactive”, surprisingly smooth and powerful” and offer to “efficiently transfer energy”. Of course all of that sounds great, but all it really needs to do is send you forward by pushing water behind you.
A personal preference of mine is a foot pocket that comes to the heel. I just don’t like it when the foot pocket stops at the halfway portion of my foot. However the ever popular Jet Fins do just that and people swear by them. I also don’t like a fin that is too long (to the point where I have trimmed my fins down myself). I feel I have more control over a shorter blade and can manage tighter turns and swimming backwards with more ease using a shorter blade.
As a sizeable piece of equipment there is that angle to think of as well. Fins take up space in your gear bag and can contribute to extra baggage fees. They are generally awkward to pack and can’t be compressed like a BCD or wetsuit. There are some great lightweight fins on the market. Even if you love the design of Jet Fins as many people do, there are similar options that weigh much less. Make sure to consider all the factors before grabbing the first pair the person in the shop shows you.
There are some clear favourites in the industry that you could start with. Mares Avanti Quatros are everywhere, Jet Fins are super popular as well. I am on my second pair (in 20 years) of the original Cressi Frogs and only had to replace my first pair because they melted when a friends dive shop burned down.
As I stated before I am not a fan of split fins so can’t offer much constructive advice on that front. But if you want to learn to swim backwards (and who doesn’t) split fins are not up to the task. I still feel like split fins are a gimmick piece of kit that somehow has managed to stick around. I have the same feeling toward the Scuba-Pro Seawing Nova, but it is very popular and I do like the construction quality. Sometimes it can be hard to account for preference. At the end of the day, if you like it and it works for your diving style, that’s all that really matters.