Strict form standing or preacher with no crazy back arching. I know curls aren't very beneficial from a chain "functional strength" standpoint. But at my age it's the one exercise I can still do with a fuck ton of weight and not have pain. I still do bench. but I have a bad impingement. so I don't go as nearly as heavy as I did in my 20's, and 30's. but I'm still curling just earlier today I did 3 sets X 10 reps with 125lbs.