Fastest way to level up heroes?

In this thread @Revelate and I explored the various merits of which heroes to train to level up quickly… mostly it was a master class by Rev on how to power level your heroes - good reading and very pertinent to this topic.

I reckon it boils down to:
If you need a special skill to increase, you need to focus on the colour of the hero. For anything else, the most efficient way to level is Tier 1 and 2 training. (Even though it’s not colour-specific, the much faster rate of churning out the fodder means net overall faster levelling of the hero.) You do Tier 2 while you have rucksacks and Tier 1 otherwise… but this presupposes that you can actually drum up enough recruits to feed the machine.

I found I just can’t sustain the recruit rate to keep up a steady supply of the Level 1 and 2 training. If you can, you produce fodder at an awesome rate. As it is I don’t play as often and find myself needing to resort to Extra cheap just because I don’t have enough recruits much of the time.

Really recommend you read the series of posts from the point I linked onwards - some good tips on which map regions to farm as well as how to balance food vs recruits vs energy. All Credit to @Revelate for that information.