From 50 - 60 then fishing regardless of f2p or member.
From 60 - 70 if you have a dragon axe, then WC yews, or fish lobbies again/monkfish
From 70 - 80 Monkfish would be fast, but then when you learn to cut magics, it can pay off.
Honestly, level is the most important thing when fishing. Can't really depict on what can actually make more money or not unless you spend the time to commit.