Just as Loli XXX said. Grace leans towards defense while Sylseth is the more offensive of the two.

Sylseth will never be a supertank. At max level on her 2AW with prince deployed and with Elyse's skill she can't tank a mithril golem. Maybe with some more buffs she might be able to pull it off, but it would require a lot of resources to get to that point while there are plenty of other units who can tank better than her without much hassle.

However in my opinion Mage Armors are not supposed to tank bosses, they are supposed to get rid of multiple enemies while also being able to hold the line against said enemies, and in this regard Sylseth is better. Mage Armors only deal AoE magic damage while they are using their skills and Sylseth's skill has unlimited duration, so she can start dishing damage from the start and never stop dealing said damage. She's durable enough to tank most enemies except the ones that would require a supertank, while also dishing respectable damage on her own and she also has the range to assist other lanes or a duelist or tank facing an enemy she can't tank. At the start of the game she can carry most maps while in the late game she is still able to pull her weight and help a lot your other magic damage dealers with her FLAT MR resistance debuff.


I have not used Grace, but what I can tell is that she's completely reliable on her skill. Without it she can only help as a blocker of multiple enemies, but she can't deal with them nor can she tank a powerful enemy without said skill. This means she requires higher knowledge to properly use, you need to have her skill available when a big boss is coming, but you might also need it to deal with a wave of multiple enemies. Since it has a rather low reuse time, I think you wouldn't have much trouble accomplishing this but is something to consider. She also has considerably less range than Sylseth and that is something you'd definitely feel. Grace however is able to tank anything with proper support WHILE her skill is up and she also comes with an MR buff to all of your melee units that is definitely worth considering.


All in all they are both great units and is up to you to decide which one to choose.
Long story short Sylseth is definitely easier to use and considering my point of view on Mage Armor usage, she's the one I would choose. However Grace is more beautiful