I'm getting into the game again, played mostly before the Career Engine was introduced. Currently I have 7 waggons, 80 speed, 5 acc and 40% reliability. Where should I go next? I was thinking of going to 90 speed and 6 acc, and then to 11 waggons. I've noticed the engine is best in the early eras (of course ;)).
And more in general for people who google this in the future (I've done that, and didn't find any clear-cut answers);
What is the Career Engine best used for and what upgrades should you focus on first?