Flint

Use him early to do campaign mode, upgrading him to 71. Because Flint is an economy hero, his skills are passive. Because of this do not reset him once he reaches level 71, but upgrade him no further.

He should be enhanced to +5, which give a +30% bonus to Gathering March speed, +10% bonus to Gathering speed, and +30% to Troop Load.

Troop Load is especially important because its the stat that specifically deals with how much your troops can carry from resource tile or warehouse to base in a single trip.

The way to think of this is to think of Troop Load as a backpack each troop carries, which can be upgraded to store more.

Thus if there are 100 food items, 10 troops and each can carry 1, it will take 10 trips to carry 100 food back to your base. However, if you upgrade their pack to carry 10 food instead of 1, each troop can carry 10 and can carry all 100 food back in a single trip.

That is why Flint should be one of the the first heroes you evolve and enhance, along with others that increase troop and rally size.

Increase Troop Size → Rally Size → Troop Load, in that order. This should be the priority for how you build your early economy heroes.