Best heroes to have in barracks?

This will depend on which heroes you have and which ones you are able to unlock and upgrade the skills for. Orange heroes are the best of course. The S (season) heroes (S1, S2 etc) are potentially the strongest, however to make them strong you have to unlock their skills and this takes duplicate heroes (for hero medals) and it can be very hard to get these, unless you play a lot or pay money.

The best orange heroes without spending a lot are the ones that you can get and unlock the skills for. Always check through the skills list though to see if they are specialised for a particular troop type (ie some skills only work when leading fighters to vehicles etc.) If you plan on using all fighters then vehicle heroes will be less useful.