In every era of Test Cricket, fast bowlers have remained soul of the game. Cricket is a contest of batsmen and bowlers, more precisely fast bowlers. From Dennis Lillie to Glenn McGrath; Fred Trueman to Ian Botham; Malcom Marshall to Curtly Ambrose; Allan Donald to Dale Steyn; Richard Hadlee to Shane Bond; Imran Khan to Waqar Younis, fast bowlers have revolved around Cricket as moth revolves around candle.
The previous eras of Test Cricket were more blissful when we had some of the best fast bowlers playing simultaneously. The charm of fast bowlers has started to dwindle, particularly the post-McGrath era has given us only handful of fast bowlers, and those[i.e Nitini, Flinroff, Bond etc] who were delight to watch in McGrath's era have also gone off.
I feel that, in current Cricket, we can see the best Test fast bowler in form of Mohammad Asif, yes! even better than Dale Steyn because Asif's panache, class, temperament, stamina is purely of Test Cricket. Its not a mere observation of mine, in fact Asif is consistently jumping the ICC Rankings and currently stand at Number Two just below Dale Steyn. He would have been number one fast bowler, in ICC Rankings, had he not faced the ban or had Pakistan played enough Test Cricket to match other Test playing nations.
Test Cricket is test of everything. Your physical and mental fitness, stamina, patience, everything is tested in this format of Cricket. For fast bowler, its not all about taking Wickets, sometimes a bowler creates more problems for batsmen even without taking wickets, that's exactly what Asif does even if he is not taking wickets. You pitch 80% balls of your spell on "corridor of uncertainty", beat batsman on same channel and then take him out with a beautiful deceiving delivery- that is Test Cricket. You savour and relish it more than a wicket, taken by Shoaib Akhtar or Brett Lee with yorker after going for sixes and fours, in ODI or T20 Cricket.
Considering Asif ahead of Steyn is because of Asif's flair which is nightmare for batsmen in Test Cricket. Styen might be the number one but panache of Steyn can be seen in Twenty20 or ODIs, as he is skiddy bowler, who usually beats batsmen by his pace but not mind. But what Asif does to batsmen can only be seen in Test Cricket and that's the charm of Test Cricket, for hardcore Cricket lovers Test Cricket is still the priority and its only because we have bowlers like Asif. He announced himself in Karachi 2006 and after that he has done everything in Srilanka, England, Australia, South Africa and New Zealand. He has been, unarguably, Pakistan's sole spearhead since 2006.
Asif steams off with his blooming run-up, crosses the umpire, rotates his arm[as he is hurling a grenade], and hits the beautiful position of seam on "corridor of uncertainty", he can nip ball back-in to nudge the stumps or get LBW, if someone does not like this then he can move the ball away to deceive batsman and be it Pietersen(Oval 2006), Dravid(Karachi 2006), Clarke(Headingely 2010), they all ended up losing their wickets caught behind as the delivery was not less than a brain-teaser.
The man has 94 wickets to his name in just 19 Tests. In last 50 years, only 6 bowlers have managed to take 100 wickets in 20 or less than 20 Tests. If Asif takes 6 wickets in next match, against England, then he would be the only 7th bowler to achieve this feat. When we dug a little deeper, we get to know that in this decade only Styen has taken 100 Wickets in 20 Matches and in last two decades only Waqar Younis and Dale Steyn have done it. So Asif can be the only 3rd bowler to achieve this feat since 1990. And with this pace, if Asif manages to play 80 to 100 matches, he would have 400 to 500 wickets under his belt.
The major forte of Asif is that he is not dependent on others to take wickets, otherwise Pakistani fielders would have never helped him in taking wickets. He mostly takes out batsmen by LBW, Clean bowled, or caught behind. In recent Test Series against Australia, Asif took 11 wickets and 6 of them were either bowled or LBW, 4 were caught behind and only wicket involved a catch from Imran Farhat. And more precisely, Asif is always there to take out cream of opposition rather than tail. Out of his 11 wickets, against Australia in recent series, 9 were of proper batsmen and 2 were of Mitchell Johnson and Tim Paine.