First off, if you just want to know which is the best, go with gun powder, with a profit of 13 and a weight of only 30 it's the best, period.

First, I went and got the value of each product at cheapest and most expensive. This way you I would know the profit.

Profit of all items at best conditions

1. Cotton or Gun Powder at 13
   
2. Rum, Tobbaco, and Spice tied at 5
   
3. Oil at 4
   
4. Sugar at 3

(this doesn't account for porting cost, and tests were done at tycoon level)

So now obviously sugar is out, and through further inspection, oil is as well. This is because it barely ever becomes a red item (maximum profit).

While doing the above experiment I wrote down the weight of 1 unit of each item, here's a list of that as well, in order.

Weight of One Unit from Least to Most

1. Oil, Rum, and Gunpowder at 30
   
2. Tobacco at 40
   
3. Sugar, Spice (and everything nice *wink wink devs*) at 50
   
4. Cotton, as the most heavy/unit at 60

Now I divided each weight by the profit and got a ratio. The closer to 1 the better.

What you've been waiting for of course from best to worst

1. Gunpowder at a ratio of 2.3 and a rank of 1
   
2. Cotton at a ratio of 4.61 and a rank of 2
   
3. Rum at a ratio of 6 even and a rank of 3
   
4. Oil at a ratio of 7.5 and a rank of 4 (although i would place this one last due to demand being low almost always)
   
5. Tobacco at a ratio of 8 even and a rank of 5
   
6. Spice at a ratio of 10 even and a rank of 6
   
7. Sugar in last place due to the massive weight but low profit, at a ratio of 16 and a rank of 7

While conducting this test I noticed it doesn't really matter how far you go for something as it doesn't change once you embark (through quicktravel of course). I also noticed this trading gets really repetetive really fast. (@devs) Maybe there could be hidden trade routes for people to find, or randomly generated ones (as long as they worked well). Just not have the items be random, maybe change weekly so then travel times matters. Or have it be sugar at some ports on even weeks and cotton on odd weeks.

And thanks everyone for reading this guide, please rate up if you liked it or learned something!

And if this is well recieved I may do another guide getting more in-depth with port pricing/port buildings