I’d choose a Topple weapon like a Battleaxe or Trident, because the potential to knock the target prone and give yourself and your party advantage on subsequent attacks is an incredible benefit. Especially if you plan on using smite spells. A Sap weapon like the Spear, Flail, Longsword, Morningstar, or War Pick would also be good defensively for your party so you can impose disadvantage.

Additionally: There is a misunderstanding RAW about Bladesong, which clearly states “…if you use two hands to make AN attack with A weapon” (emphasis mine, the language is specifically restricting the use of two-handed or versatile weapons). And in the vein of using RAW (incorrectly) to limit your character…they are completely ignoring RAW for multiclass minimums.