I think it just depends on what your goal is. Some people try to earn as much cash as possible to decorate the farm really fancy, or buy a new machine. In that case, make your own stuff and sell it instead of buying. If you want to level up as quickly as possible, filling boat and truck orders as fast as you can, by whatever means (like buying from the newspaper) works best. You won't be super profitable, but that's ok. The endgame is just to have fun...so play it however you want to! That's my opinion at least. And I am on level 56 and it is working just fine for me.
