Video I've seen on making units fast say to make and sell Liquid Explosive.

Liquid Explosive is worth 1,000,500. It's made from Acid and Unstable Gel
For those you need Mordite, Fungal Mould, and Cactus Flesh.
It takes 120 minute to farm Cactus Flesh.

Now look at Living Glass. It's made from Lubricant and Glass.
For those you need Coprite, Gamma Root, and Frost Crystal.
Farming time is only 30 minutes.

It looks like I should be able to make Living Glass at 4 times the rate of Liquid Explosive.
Living Glass is worth 696,000 x 4 = 2,784,000
That's 2.783x the value of 1 Liquid Explosive.

So I hadn't taken into account the size of the farm needed for a single product of each since I didn't have data on how many of each resource is produced by the different plants. Now that I've been playing with Geodomes I reevaluated my earlier calculation.

Living Glass requires 250 Frost Crystal, 50 Coprite, and 400 Gamma Root.
Frost Crystal is 50 per plant, harvested twice, and requires 3 plants.
Coprite is 25 per plant, requires 2 plants.
Gamma Root is 50 per plant, requires 8 plants.
That's 13 plants, leaving 3 slots in a Geodome.

Liquid Explosive requires 200 Cactus Flesh, 25 Mordite, and 600 Fungal Mould.
Cactus Flesh is 100 per plant, requires 2 plants.
Mordite is 25 per plant, requires 1 plant.
Fungal Mould is 50 per plant, harvested 4 times, requires 3 plants.
That's 6 plants. Mordite can be harvested twice and the other plants tripped for 16 plants.

With one more Mordite plant, 3 products of Liquid Explosive can be produced in 120 minute.
1,000,500 * 3 = 3,001,500

For the space of nearly 1 Geodome, Liquid Explosive is more profitable by 217,500 units.

The most profitable item is one with the highest hourly rate profit. It's probably one that you can farm easily (quick grow rate) and sell for a 5-figure price. Nipnip was the one in Pathfinder.

Interesting. I don't have Mordite as a plantable item since restarting from the beginning in 1.3 and then grinding through the specialist terminals. Even tried recalling the Farmer and got a request to replant the Grav Ball but after that he/she/they went into the ending "three hour lecture" monolog.

Not sure how useful large-scale farming will be, now that the hydropontic planters need to be recharged periodically. Feeding the 60+ plants in my Pathfinder-level greenhouse would be a bit of a pain.

The glass dome structure takes care of the plants, no need to run back to recharge the seed box

Ah! Good to know. Thanks!

Have you noticed that repeated visits to the same Trade Terminal with the same load of [pick your favorite commodity] results in a noticable drop in the price paid? That's rather annoying. Can't just grind out units and make trips to your favorite space station without being penalized by price reductions. Grrrr...

Wonder if the same thing happens with a local (in one's base) trade terminal? I haven't taken the time to collect the resources to construct one but constant price cuts would be a strong argument against having one's own terminal.

The most profitable items are the stasis device and the fusion ignitor. They are advanced crafting blueprints found in operation centers and manufacturing centers. They both sell for ~18,000,000 each.

As for the trade terminal stock levels, these have been reverted/improved in the experimental channel and resupply over time.

The set up that's working for me at the moment, if anyone wants to give it a go, is this:

Construct 4 biodomes at your base... I set up on a Lush planet specifically so I could plant star bulb brambles outside and not have to provide any kind of planters for them. In the biodomes I'm growing the following:

12 Solar vines
6 Frostwort
7 Echinocactus
24 Fungal Clusters
1 Mordite root
24 Star Brambles (growing outside)

This gives exactly the right resources to craft:

3 heat capactitors + 3 poly fibre = 3 circuit boards
2 acid + 2 unstable gel = 2 liquid explosive

which altogether sell for about 5.5 million

It's definitely not the most efficient way of making money as you're waiting on the solar vine to grow for 2 hours, but if you don't want to be a total slave to the grind it's good to be able to swing by the base ever two hours and grab the cash. A good balance of profitable farming and exploration time I feel.

The initial outlay is pretty high for the biodomes, and you'll need to stockpile a fair bit of thamium for all those plants, but it's not too bad.