It surprised me that there is no topic like this already here. I think my best chance is electronics or gambling, because with gambling at least my budget can be in the green, but i never got my other casinos to be successful
without a doubt the money would be in electronics, selling TVs. you can recycle to make alloys and plastics for your factories or you can even import alloys/plastics and still make a great profit selling your product. another benefit is that you can plot these buildings anywhere you want.
if you go the drilling/mining route youre limited to resources on the map AND the resouces can be depleted; you would have to re-plot the the drills/mines when resources run out
plop a vu tower next to your industrial so they can increase in tech. plop down a processor factory and a trade depot. import plastic and alloy and export processors. go afk for build/re-build your city. come back with 1 mil simoleans and build a couple more processor factories til you can upgrade the HQ and then start building computers. after a while you should have the other trade depot unlocked and have everything imported and exported by train or boat. you can get 10mil simoleans in an hour.
How many trade ports / depots do you need, and how many processor/ tv factories do you need? I have seen videos that have like 7 processor factories, but doesn't explain how it works, or how many trade ports you need. Please do not link me to a 25 part series video list where each video is 20 min long