Best Lego train? I wouldn't know where to start! I enjoy passenger trains more than goods trains, so this is my line of thinking:
TLC got serious with trains when they launched the grey 12V series in 1980. No less than four motorised trains were released! Three more battery-powered or push along sets! Many more carriages, new track and electronics, they really went all-in and created a complete, fantastic railway experience. And of course at the forefront of the grey-track revolution was the 7740 Inter-City. It was the biggest set of the year, and a substantial gamble for Lego to take. A faithful reproduction of the DB Class 103 electric locomotive, it came with two carriages, ten minifigs, a platform and loop of track (sets sold in Australia at the time even came with a bonus transformer, everything you need!).
The 7740 really paved the way for the next great passenger train sets - the 7745 and 4558 both followed this path very closely. The 4558 Metroliner was the first of the 9V trains, and Lego again went all-out to create a realistic, detailed train set that both kids and adults could appreciate. Of course the 9V system crushed the dreams of the 12V fans who were looking for new sets after being left out in 1990. (I still remember the moment I saw the new trains in the '91 catalogue. )
But I won't let that detract from the fact that the Metroliner was a brilliant kit and it wasn't until over 10 years later that TLC again did something special, this time with the Santa Fe Super Chief and it's array of passenger cars. With plans for no less than 5 different passenger carriages available, the Chief and it's gang are awe-inspiring to look at.
And of course this year, train fans were again blessed with the arrival of the Emerald Night. Another brilliantly designed set for another new power system, the smooth lines of the EN almost make it's predecessors look blocky. Almost.
So there you have four fantastic sets, each one the commander of it's era. Is it possible to pick a single winner out of them? I'm not sure I'd want to.