Suggesting proper fins for someone is very hard. Fins are one of the most personal parts of the equipment, they need to match well to:
- the anatomy of your body
- the kicking technique you use
- the amount of drag you have to win (which depends on your remaining equipment, and also on your trim)
The first demands for a certain ratio between length, stiffness, and angle between the blade and the sole (which is depending on how much your ankles can extend during rotation).
The second dictates the choice among different types of fin: for frog kicking, the usage of long and flexible freediving fins is not recommended.
The third dictates the "gear ratio" of the fins to be used. It is like on a bicycle, climbing a steep hill is better done with a short gear ratio, while for running fast in the chronometer one-hour race in plan you need a much longer ratio...
What explained above can be the starting point for orienting you, but in the end only testing them in real usage scenario will confirm that the fins are good for you.
My wife was always remaining behind from me, and she did buy at least 10 pairs of fins, until she did find those that allowed her to not only keeping my pace, but surpassing me easily, and end the dive having used much less air than me.
It turned out that here legs are strong, but she cannot sustain an high rhythm, so she needs fins which are long and stiff, to be operated very slowly: full-pocket free-diving fins, choosing the hardest of the three available blades. Not very fast, but very efficient.
But, as said, this is a very personal choice, what is good for her is probably wrong for you. All the advice based on other people having found what is optimal for them, is of little value for you, as every body is different (and the kicking style is also very important).
So I can only suggest you to find the way of testing at least 10-12 pairs of different fins, then you choose.
Last point: have you considered taking a class with a finned swim instructor? Both I and my wife are finned swim instructors, and, as said, the kicking technique is also a very important factor for proceeding in water with minimal effort and proper speed. Also breathing is involved, as with improper breathing you accumulate CO2 and this causes cramps...
Most diving instructors have no previous experience as finned swimming athletes, or as deep free divers, so they do not give a lot of importance to optimising the various kicking styles. I do not know if in your area there are clubs practising finned swimming. This is where usually you find these instructors...
And where you will be allowed to test dozens of different types of fins... Possibly all of small sizes, as usually finned swimming is an activity practised by children and youngsters, so they all have little-size, very powerful fins.