I currently have Kutchen fully leveled and at lev 18 on class tree, is the 2% mana boost worth it over the crit chance, i have level 26 mana troops so when they max out will the 2% even help me? Or is it even worth going to level 20 on the tree at all?
Note: I have no mana boosting heros on my main team as it is comprised of Kutchen, Gravemaker, Vela, Zeline and Drakefong. Thnx for the advice 
Typically the Crit chance is of more benefit, but I would suggest you check out the Optimal Mana boost thread and determine if this extra 2% will help boost you to charging with less tiles: Optimal Mana Bonus Numbers for Every Mana Speed (Now including Ninja Heroes)
Sometimes cutting off that extra tile is great (ex. Moving an average hero to charging in 9 tiles) but with a slow guy moving from 12 to 11 tiles still means you are usually charging by matching sets of three so it is not as huge a difference.