Sometimes I get the feeling that Asif is lazy(not unlike myself), but when he keeps getting constant breakthroughs I somewhat feel injustice done to him on that behalf, and that sort of makes me feel that Asif is better than Steyn ever-so-slightly, if you really need a breakthrough quickly. Another feature of Asif is that he can get an old ball to swing quite a lot if there is anything in the pitch at all. But with the new ball, Steyn > Asif. And Steyn is slightly more durable that Asif at times, and against Sehwag you need two qualities, Wits and Patience, two of which Asif has. So to cut it short, I think Asif will be slightly more successful than Steyn given a slightly juicy track in the middle/end of an innings, and vice versa at the start, especially as Steyn fires them in with a hint of swing and a hint of accuracy.