Barbarian fishing is not the fastest, C2 fishing is. For cash, Rocktails are the best, but if Monkfish/Lobsters are your only choice I would go for Monkfish, though Fishing in order to make cash is generally a bad idea.
C2? I'm only level 73 trying to get all skills to at least 80. But I wanna make cash while doing it. Or enough cash to fund other skills such as smithing and crafting.
Lobbies/swordfish is a bad idea. Monkfish are better but would be slow at your level. As CreativeNub said, fishing is bad money. I'd say do barb fishing to get it over and done with and you can use the time you saved from doing barb fishing to do money making.
all depends on your lvl .. you would have alot better luck with accurate answers given you fill us in on your lvl.. GL regardless at high lvls monkfishing can be good xp and decent gp. Alching the fish as you catch them barb fishing is the absolute fastest xp/hr though
Monkfish forsure. I personally was doing monkfishes for about 20 levels and i made more cash than lobsters and sharks.
Also it was much faster then sharks.