I have my Genasi Assault Swordmage (Elemental Tempest) at 12th these days and love him. I'm still with a Longsword to keep my defenses highest and I have resistances out the wazoo. Why I kept the longsword was a: feat allocation and b: the mentioned AC. He has a good deal of teleport powers and loves to see the classic Big Bad Artillery with brutal meatshields/soldiers up front. He just gets in to the backfield and goes after the artillery when the meatshields engange, not even trying to use his mark to teleport. Let the Necromancer step off an shoot him, I'm resisting Necrotic, etc. I keep the rest of the party from eating his nasty spells while resisting a good deal of the damage when he does hit.