Darui for sure. Asuma is more muscular but I don't think he is stronger at all, his wind technquies were quite average (weak IMO) and he wasn't much of a challenge. Asuma lack variety, speed, intelligence and wasn't swift at all. Now, though we have not seen much of Darui, he strength of display has been very impressive! He has water and strong lightning tech., which he can convert into a big storm (BA) and has special black lighting. Also, he has pretty good physical strength wielding his huge sword and has shown he has some intelligence as he figured out Kin/Gin's sealing tricks. Darui wins with some difficulty.