Smaller jet in this game in general are a lot more profitable (per passenger). The problem though, is that you will eventually hit lot limit so you will be forced to upgrade to larger aircrafts
In late game, the main objective would be to transport as many passengers as you can to dominate in countries therefore profitability though still very important, might not be the only factor to consider
Oh also, i might tweak the airplane category every now and then, but my plan is to make it more transparent to user (in the aircraft info) instead of being hidden like now
My favorite:
Boeing 737 MAX 9 - I have almost 200 of them and still ordering more