A high leveled mana troop is highly benefical to have as it would lower the amount of required tiles to charge a hero by 1. I have multiple 4* troops but the only ones over lv12 are the mana ones, wich are respectively at lv 30 
/29 
/29 
/29 
/25 
Here you can see a detailed guide about troop’s leveling: Troop Guide and Levelling Suggestions
Crit troop can also be useful but the mana ones grant you faster and hard hitting heroes, so apart from titan’s battles and PvE I generally use mana troops.