Most early-game cash the fastest, with the least investment, and disregarding every other consideration?
Fishing. Hands down. You can make over a hundred thousand in your first spring by fishing. I wouldn't suggest it, because the only thing you'll be doing is fishing, and while it is an enormous early-game cash cow, farming will later on surpass it if you have the farming levels invested. But if that is your only consideration, then head to the mountain lake and be a Pro Bass Fisher.
Most profit per transaction in Summer? Hops, hands down. More profitable than melons, more profitable even than Starfruit. Pale Ale is (these days) the single most profitable thing you can do in Summer.
In fall, it's either pumpkins or cranberries. Pumpkins are less hassle, but there is something to be said in drowning the world in cranberry sauce.
Fun fact: Did you know that Ancient Fruit is not the most profitable crop to have in your greenhouse? That award goes to Peach and Pomegranate trees, and it isn't even close. The second most profitable? Hops. It requires daily tending, of course, so there's a time investment to be made, but it easily falls in number two slot. Number three is Ancient Fruit, with a caveat that there is a specific late-game strategy using materials only obtainable during Qi Quests that might theoretically push Starfruit past, but given the enormous pain, I'm electing to ignore it.
So once you get the greenhouse unlocked, you will have a choice: Do you wish to go for the 'easy' strategy of just planting an entire plot of Ancient Fruit, and have a one day workweek, or go for the more profitable method of planing 30 peach/pomegranate trees, then 74 hops, then another 30 ancient fruit as infill around the more profitable crops that you can't walk through?
Also, that note on the wiki about preserves jars is extremely misleading. Technically, it is factually correct, you get more g per day with preserves jars, barring the two outliers. However, because this higher gain is amortized over a shorter period of growth, you realize lower profits in total at the end of the quarter in many cases. There are some cases, mostly vegetables, where turning them into preserves is the more profitable option. There are others, generally low-cost produce, that there is very little if any difference, in which case the faster iteration of the preserves jars means lower infrastructure investment for the same yield. However, if you truly wish to maximize your quarterly profits, kegs are the undisputed king when paired with high value fruits like Starfruit, Ancient Fruit, Hops, and yes, peaches and pomegranates.
The choice, as always, is yours.
