Let’s do some math:
So, if you farm on 8-7, you can have 18-20 recruits per hour. If you deviate to other provinces, the average can drop to 10. Let’s assume 10 recruits per hour, so for 2 day the budget will be 480 recruits.
Let’s have some other math to figure out recruit costs for the same period of time (2 days):
TC20 takes 100 recruits per 2 days
TC13 takes 80 recruits per 2 days
TC11 takes 2 recruits for 2 hours = 48 recruits per 2 days
TC1 takes 5 recruits for 10 minutes = 1440 recruits per 2 days
TC2 takes 5 recruits for 30 minutes = 480 recruits per 2 days
TC4 takes 4 recruits for 3 hours = 64 recruits per 2 days
TC5-8 takes 5 recruits for 1 hour = 240 recruits per 2 days
So, to actually keep your 4 TC busy, you need to choose TC levels so they won’t be more than your 480 recruits per 2 day budget.
So, basically, you can’t run TC1 or TC2 all the time at all! You can run them to burn through excess of recruits, but then switch to TC11/TC4/TC5-8.
If you run TC20, you can also have TC5-8 and TC4 and still accumulate recruits.
If you want best hero per recruit ratio, you need to aim to TC19 and TC11, since they give you 1 hero per 2 recruit. If you’re recruit-bound and not meat-bound or material-bound, that’s a good solution.
Personally, I used to run 2 TC20 and 2 TC11, switching one from time to time to TC19 to burn extra recruits. I wouldn’t advise running TC1 at all, since TC3 is much better if you do have enough meat.
Right now I have one TC20 running and 3 TC11, one of them I switch either to TC3 or TC19 for an hour or so, depending on what materials I have on my hands.