Your thread title "Best full-foot fins" begs the questions "best for whom?" and "best for what?" We're all different, with different likes, needs and expectations. The first full-foot fins were Cressi Rondines, invented in Europe by Luigi Ferraro, and this classic design has been endlessly imitated and is a particular favourite of mine:
Rondine Fins | Luigi Ferraro
Fin choice is part scientific and part cultural. I do expect my full-foot fins - and I only wear full-foot fins when I snorkel in the cold water of the North Sea - to complement the gentle style of sculling I now embrace in my 60s. I would expect them to give me extra power, manoeuvrability and endurance, the scientific aspect. However, I also want them to look simple and straightforward with a sleek, classic design. Too many modern full-foot fins look like this:
To me these fins look gimmicky, a dogs' dinner of different materials and a shape that makes them look as if they've been through a mincer and as though their blades have been well gnawed by rodents. I'm sure people will say that such fins are incredibly light for travel use, but why should I let an airline choose what fins I wear? I'd rather stay at home and snorkel in local waters, and that's what I do.
As a traditionalist, I prefer all-rubber full-foot fins in solid colours, with enough blade stiffness to propel me through the waves. Here are some of my favourites:
Gull Hard Mew
Escualo Clasica
Scubapro Rubber Full Foot Fins
Oceanways Aquapro
Balco Sprint
There are others, but the above are all comfortable, fit for purpose fins from my personal perspective. However, returning to the title of this thread, they're best for me and the kind of snorkelling I do. That doesn't mean that they are best for anybody else or for every kind of water activity. Finding the best full-foot fin is something of an odyssey. It took me a while before I chanced on pairs that match my foot dimensions in terms of width and height as well as length. There are no instant solutions, but the ideal pair of full-foot fins, once discovered by each individual, is a joy forever. I would never go back to open-heels. And to those who say that full-foots can only be worn barefoot, I say "nonsense". The Japanese, who like me prefer all-rubber full-foot fins, wear them with booties. You just have to wear the booties at the time of purchase and select a big enough foot pocket size. Works for me too.