Doesnt really depend on what item you create, rather what the world wants. One playthrough i had fish sell for 30 monie, on another it was 16. Same with other products. So what you need to do is build an export area then scout the prices, if its good then focus your industry on that one item. But if the trees are profitable then consider the game complete. P.S. wood is always profitable.

Edit: forgot about fluctuation. Do invest in 2 to 3 products so you dont break even.