You are aware that you don't have to choose between smite spells and divine smite? If you have set divine smites to "ask" then every time you hit a target with a smite spell you will be asked if you want to add a divine smite on top.
This certainly burns your spell slots, but allows you to deal a ton of damage quickly.
It is especially powerful when combined with an item that ensures a critical hit. Then you can deal 14d8 radiant damage (+ whatever damage your weapon does) with a single hit.
