Since both Gravemaker and Clarissa are very fast mana generating heroes, it would be logical for GM to opt for the defense multiplier bonus as the 19th node, but for Clarissa, personally, I would opt for the crit bonus as the 19th node. An addition of 2% mana bonus for very fast heroes are almost negligible already.
Personally i go for mana bonus, because i only have 1 mana troop above lv.11.
In case if i get 2nd gravemaker, with GM emblem +19 on mana node i can build another mana troop only to lv. 5 and give it to GM +19 and he can still charge in 3 tiles.
Meanwhile the mana troop above lv.11 can be used by my 2nd GM.
So in the end i will get 2 GM that can charge in 3 tiles.
Basically it is all about ur mana troops roster.
If u can afford to get 2 mana troops lv.11 of the same color (if someday u get 2nd GM), then just ignore embelms +19 on mana node path and choose defense instead.
or Grazul… he can be use stack with mana troop,… and also maybe another red avarage heroes, etc…
I agree, it depend on mana troop and who to use frequently in red stack.
Also the same case for Clarissa.