This is good rail description.
Where do you surf and how do you want it to surf are probably good things to figure out to help with what wil suit you and the waves you surf best.
www.boardcave.com/the-surfers-corner/surfboard-shapes-tails-rails-and-noses/Finally, the general foil of your rail will make a difference in performance.
The exact foil of your rail can be different in each model, however there are a few trusted foils generally used, which are 50/50, 60/40 and 80/20. This relates to where the apex of the rail is around the curve.
A 50/50 foil is found in more soft rail options and traditionally on longboards.
A 60/40 rail is going to be turned down with the apex slightly under the middle of the curve of the rail.
This type of rail can be blended into both soft and hard rails and is also a great option on smaller wave grovelers, fish and fun boards options. They generally give you a good blend of maneuverability and stability.
The next style, the 80/20 rail, is when the apex is even closer to the bottom of the board.
These rails are commonly found on high performance boards and usually incorporate a hard edge - hard rail when getting closer to the tail. These are made for easy maneuvering and rail to rail surfing as well as performance through turns.