When I only had 4* heroes to work with, my general-purpose attack team was Tiburtus - Sonya - Boldtusk - Chao - Little John. With that team, I finished all of Season 1 and could raid up to about 2300 trophies. More info here:
On defense, I’ve heard that Kashhrek and Boril are generally the best options for the tank slot. Depending on which one you go with, I might recommend something like this:
Sonya - Tiburtus - Kashhrek - Li Xiu - Kelile
or
Caedmon - Boldtusk - Boril - Tiburtus - Chao
With those setups, fast dispellers are on the left (to eliminate riposte), then an attack increaser, then tank, then two hitters for the bulk of the damage output.
All recommendations are assuming TC20 heroes only, but event/Atlantis heroes can improve these teams with their different abilities, too.