OpenTTD 12.0-RC1
The best game in the "transport simulation" genre that i've played would probably be Transport Fever 2 (https://www.transportfever2.com/), because it not only looks better when compared to everything else out there, but the UI also feels really streamlined.That said, OpenTTD is also amazing because it's free, has a lot of lovely content and definitely provides plenty of replay value, in addition to not requiring a beefy computer (unlike the aforementioned game).Some other similar games that people might enjoy:  - Simutrans (https://www.simutrans.com/en/) is another transport simulation game, which has a lot of different tilesets, but the actual gameplay of which seems to be a bit less enjoyable than that of OpenTTD and others, though it's also freeware
  - Mashinky (https://www.mashinky.com/) is an indie game that mostly focuses on trains, but also is in 3D and looks pretty good, like Transport Fever, though some people say that the economy in the game is a tad odd

I've also heard of Cities in Motion and Railway Empire, though haven't played them myself.