Choosing fins can be quite complicated. There are poor fins and excellent fins, but knowing what to buy, from what company and what type (freeride, slalom, course slalom, formula, freestyle, speed and wave) all gets quite complex.
There are several excellent custom fin companies, all making a wide range of fins that offer a high level of performance for every size board, sail and sailor.
Most beginner, novice and some intermediate sailors won't be able to tell the difference between a poor, average or good fin, so the custom fins are geared toward the advanced and expert sailors, who can appreciate and tell the difference.
The custom fins are quite expensive ranging from $200 to $800 US. There are also lots of less expensive "molded" fins that are quite good for some types of sailing.
For example - Tectonics makes 6 different slalom and course slalom fins, with up to 19 different length choices for their new Talon slalom fin. Figuring out which design of their six slalom fins and what length would best suit a particular need takes some knowledge, research and counseling to get it right. I have no affiliation with this company in any way, but I have one of their fins and think it is excellent.
Personal "feel" also part of the issue, with differing opinions regarding the same fin from comparable experts, so testing will be somewhat subjective much like board and sail tests.
The point is that it is all very complex and it is incumbent upon the sailor to do the research for their particular need. This forum is one good source for information if you search the archives or ask a question.
Formula 160; iSonic 111; HiFly Move 105; Tiga 263; '85 Mistral Superlight.
Maui Sails TR 11.0; 9.2; 8.4; 7.6; 6.6; Maui Sails Switch 6.0; 5.2; Maui Sails Global 4.5; 4.0.