4* Troops + Tarlak

[Kerridoc]

There is a LOT of info and opinions about troops in this old but still valuable thread:

4* troops - mana or crit?

There are two varieties of four star troops: those that add critical or those that add mana. I realize that any four-star troop is a luxury, but in the happy circumstance where both varieties are available, what do you prefer? Why?