What I do is keep a TC20 running, 2 TC13’s, and 1 TC2. But the 2 13’s I just have doing the low cost. Obviously the 20 is running chance for legendary and then I use the 2 to train common and uncommon. That’s just how I do it.
I have 1 perma 13 which gives me a piece of garbage each 2 days but they re useful to me til I get better heroes. It’s useful also as food store and for recruits food balance exchanges.
Other is at 11, providing 12 fodder heroes per day. It’s very useful as coin box for troops and food.
I switch the last one depending on the situation:
If I am very active and high on food I run tc 1,2 or 3 depending of the moment: high speed at AR event is nice. One of these 3 is running whenever I’m high on food and filling chests.
If I am working I usually switch to a 2nd tc11 It is not a problem to cancel a 2 hours train for the switch. I always have 5 heros leveling so don’t consider colour training (It’s cheaper feeding a 2k food 1 backpack Nash to a Grimm than spending 4 times more on an Olaf.
I plan to do the same at Tc 20: IMHO food and activity are the keys for a choice
Currently I have 3x TC20 and 1x TC11 running for getting some 5 star heroes. But, when I am on a hero leveling spree, I usually do 3x TC11 and 1x TC1/2/19 depending on what resources I have.
If you run 3x TC11 and 1xTC2 you will be getting 84 feeders per day. So if you do colour specific feeding you can max one rainbow 4 star team from scratch in about 20 days. If you throw in a few TC19 during this period it can be even less.