How to choose? The original RRT is downright addictive, despite the primitive graphics. RRT 3 is a flawed gem- great gameplay and graphics, but no ability to excavate to lay track, and way too few locomotives. Even using the cheat, there just aren't the locomotives you want/need without really "cheating" and buying the late-game world beaters. And the "disappearing cars" thing. One would think that the coal mine would eventually run out of wagons, since the locomotive is 'running light' enroute to the mine every time.
If somebody could combine the graphics engine from SimCity 4, the content from OpenTTD, and the gameplay from RRT 1/RRT3, they'd have a world beater.