Si, full foot: It depends. They are not as warm as the open heel, plus are you going to be boat diving in an region where it is hard to run a dedicated dive boat, so, dive boats tend to be fishing boats? There are a lot of places on our planet where we rent a fisherman’s time and boat for the day. Here is the prudent rule: If that is any kind of fishing boat, leave the full footie in the bag. Other similar "working boat" situations, follow that guideline.
Having said that, if the water is warmer, you will find some "old school" divers who feel that the full foot is a better dive - it is lighter and more hydrodynamic. Yet not everybody lives in a home that has a coral reef in their backyard, so the open heel boot also gives you the option of picking how thick you need that boot to be. You can even have several sets and sole thicknesses tucked away somewhere.
There is also a cultural factor going on here; returning to the USA after living and diving in the Western Pacific for about 20 years, I was "charmed" by the amount of gear that a significant number of divers in the USA wear for a "typical dive." All these redundant systems. It is quite the trend. Not everybody has moved in that direction. There is an influence from tech and military diving that is more affective in some countries over others. If you dive and also come from a country that doesn’t happen to have a huge navy, then the influence of the modern "Navy Look" might not be so important to you. How in the world does that relate to the question of open heel closed heel? Well, are you a "more gear" or "less gear" diver? Fact: if the water is warm and there are no rusty fish hooks on deck, the full foot, closed heel is a wonderful dive, but it is part of the "less gear is better" mindset.
This old squid, me, still likes a sunny, warm, 15 meter saunter through a coral canyon, so if I can find a dive where I can put on my Cressi’s, I will do it. However, the trend in the market today is to encourage me to kit up as if I were doing a 45 meter dive to disarm a live torpedo in a sunken submarine on "every dive," so I will certainly need to dive in a pair of solid diving "boots." Yet, considering the depths and type of water that I actually like, and my old school mentality of, "less gear is better," and hydrodynamic is better, I kit up my Cressi Sub full footie whenever I can. And, when I enjoy some free diving, that is a more "naked" feel. Cressi Sub and Mares have wonderful options. If you practice free diving in a pool, where are your full footies already? On the beaches of Southern Cal, Zuma, etc., the full foot is still pretty cool, but longer times at depth even in California, you would be surprised how cold that water is.