Planeshift is faster and tankier, and he's also undead, upgraded health and teleport he has 58 base hp that he can move at 9 speed with teleport and doing good damage and with some control with snare. Swordmage is super squishy and he's only good to throw some encouraged magic bombs, because he isn't resilient enough to endure in the front, only in witches, for obvious reasons, he finds a place above planeshift. But if you are lacking a defense counter that you need badly you can try with swordmage.
Tbh evasive, 7 speed and an extra rank of teleport for only 3 more nora makes the planeshift better in my eyes. Plus 7 speed means he can teleport and attack each turn. Swordmage uses fear as a defense. Compared to evasive it costs ap, has a cooldown, is a melee defense (not as good as ranged really) and is one of the most countered defenses in the game. I'd say the Swordmage is superior in witch BGs for his defense removal. But that's about it.
