One of the players in my group did that. I thought he was a fighter, but turns out he's a wizard; but with I guess one level of F. He'll still get access to Wish, so there's that.I don’t know about it being “the best multiclass build,” but taking your first level in Fighter is amazing for a Bladesinger wizard. You get higher starting HP, Second Wind, a fighting style (Dueling if you want to use a rapier and keep one hand free, defense if you want to pump your AC as high as humanly possible, or dual-wielding if you want to maximize your DPR), and most crucially, proficiency in Con saves. All at the low cost of delaying your Wizard progression by one level, and if you go all the way to 20th level, missing your capstone. Well worth it in my opinion.