A comprehensive guide on how to use your Training Camps (TCs) and Hero Academy (HA), backed up with maths and numbers from the “Empires and Puzzles calculator” app (download at https://play.google.com/store/apps/details?id=com.jaroderoose.empiresandpuzzlescalculator). More info on what the levels exactly do, you can find here (Training Camp | Empires and Puzzles Wiki | Fandom)
Summary
Make sure to always use TC11 and HA7, even when low on food and recruits. If you have Adventure Kits, prioritize TC2. If you have a lot of recruits, use TC1. If you have a lot of food, use TC19, HA1. If you have a lot of food, recruits and Strong Rope in the bank, use HA3.
Try to use TC1, TC19 and HA1 on 3* and 4* hero’s, and reserve TC2 and HA3 on 5* hero’s.
Training camp level breakdown
TC11 is the most resource (= food and recruits) efficient option and we will be using it as a reference. Using one TC11, it takes 15122k food and 2508 recruits to get a 5 star hero from (ascension)1/(level)1 to 4/80, and 104 days. Let’s go over all levels
TC1 takes most recruits out of all training options (4.5x of what TC11 takes) and quite a bit of food (x1.8 of TC11). In return, TC1 is the fastest way to train (x6.7 faster than TC11), except for the true speed options (TC19, HA1, HA3)
TC2 is basically the same as TC11, but 4x faster and requires 2.5x the recruits. It is one of the best training options, but adventure kits might run out
TC3 is very similar to TC19 (see later), but requires way more recruits. If your training camp is build out enough, use TC19 instead
TC4 is similar but in every way inferior to TC11. If your training camp is build out enough, use TC11 instead.
TC5-9 is similar to TC2, but you are sure which element you will pull. Using hero’s of the same element to train with gives you a 20% bonus in xp. However, TC5-9 needs 4.2x more food than TC2, and takes twice as long, meaning it is inferior in every way (except it takes slightly less recruits) to TC2. I heavily recommend never using these levels.
TC10 is used to get a chance to pull 3* hero’s, don’t use it for training. Also, I personally suggest waiting until TC12, for a 100% chance for a 3* hero, and in the meantime spending your training camps time more efficiently.
TC11 is the best option in terms of resources, but it takes a long long time to train your hero’s.
TC12 is used to pull 3* hero’s, don’t use it for training/
TC13 is used to pull 3* hero’s and a very tiny chance (5%?) to get a 4* hero, don’t use it for training. If you are full on 3* hero’s, I personally suggest not running this level anymore, instead running TC11 to level the hero’s you do have, since pulling a 4* hero here is really rare, and it takes a lot of time
TC14-18 is used to get a chance to pull 3* hero’s, don’t use it for training.
TC19 is a power leveling (speed) option which requires little recruits. It requires 35827k food, or 2.4x the food that TC11 needs and 1.8x the recruits of TC11. As a reference, active players with all level 20 farms can easily gather 2000k food in a day (you can simulate this for your scenario using the same app), so every 18 days you gather the food to power level a 5* hero using TC19 (in the theoretical case where you don’t use your food for anything else).
TC20 is used to get a chance to pull 5* hero’s, don’t use it for training.
Hero academy level breakdown
Only HA1, HA3 and HA7 are usable to train hero’s effectively, let’s go over them
HA1 is a power leveling option, very similar to TC19. It consumes half the recruits of TC19 and costs a little less food. However, as items, it requires 2 practice swords instead of rugged clothes. Practice swords are also needed for TC1, one of the better options in terms of speed. If practice swords are running out, I suggest taking TC19 over HA3
HA3 is a power leveling option, which can best be compared to TC19. It requires x1.5 times the recruits of TC19, but only little over half the food! This comes from the fact that it has guaranteed 2* hero’s, which give a lot of xp per training. Since your hero consumes food per training, you save a lot of food if you have too do relatively little trainings. HA3 is an excellent power training option, and is often limited by the amount of Strong Rope you can gather.
HA7 is a slow training option, comparable to TC11 (1.08x faster than TC11). It requires similar food than TC11, but 3x the recruits. However, you will barely feel this recruit drain, due to its slow nature. HA7 is an excellent option to always be running, similar to TC11. You leave the trainer hero’s uncollected, until you catch a nice 5* hero you want to level as fast as you can.
Difference between training 3 star or 5star hero’s
The main difference between leveling different star hero’s (except the raw amount of xp of course), is the food the hero requires to do a training, with 5* hero’s costing notoriously much food (5k to 13k per training) against the cheaper 3* hero’s (2.1k to 5k per training).
Therefor, when training 5* hero’s, you ideally want to reduce the amount of trainings you have to do to max your hero, meaning you wish to use 2* hero’s to train with instead of 1* hero’s. That is why it is beneficial to use TC2, HA3 and HA7 (which grant you higher chances of 2* hero’s/trainer hero’s) for 5* hero’s, and use TC1 and TC19/HA1 for 3 or 4* hero’s. (Unless of course you ether lack 5* hero’s, or have a lot of Adventure Kits).
Conlusion
Thank you for reading this rather long post, and read the summary again to remember what to actually do 
hope this helps!