I have leveled both for the Mastery but no one needs two Heavy Weapons that deal primarily slash damge so I'm deciding which to keep and which to get rid of. Unfortunately all of the comparisons I can find use old statistics for the weapons and/or melee 1.0 information and as such aren't helpful.
As of Update 15.5, Scindo and Gram do the same amount of damage on all attacks, have the same channeling damage and cost, the same stamina usage, the same critical chance, have the same polarity and use the same stances.
Gram - has higher stauts chance (15% v 10%), a better critical multiplier (2.0x v 1.5x) and better speed (0.950 v 0.917).
Scindo - has the damage better centralized on Slash (80 v 70) and the Manticore skin (115 attack and 0.779 attack speed).
So, which is better?
Since I had to remove the first response due to this problem I will remoind everyone here...
This is not a what's the best heavy melee discussion and any comments discussing/advocating weapons other than Scindo and Gram will be removed.
Scindo: 10% faster attack speed, can hit all enemies with one hit instead of only 3, can use manticore axe skin, has a primed version
Gram: looks badass, little better crit dmg
all other points are not important enough to mention, so i recommend you to farm scindo prime- but even the normal version is better than the gram (for me the important argument is that you can hit more then 3 enemies with one blow which is very important for infested missions - and tbh there is no other reason to carry a heavy melee ;) )
But once you get your hands on the scindo prime, get rid of both normal weapons!