Funny how these things go around..a few weeks back South Africa was not even part of the conversation..Steyn was considered finished and the rest were forgotten.
Again like the conversation about best team currently or best spinner currently, it really depends on the right conditions and factors. The most balanced attack is probably England with Stokes a 140+ bowler effectively their 5th bowler, and yet other than Anderson and to an extent Broad, you have to question the effectiveness of this attack in Asia.
Australia has a really strong attack with two extremely potent strike bowlers and in their conditions, the best attack.
South Africa and Pakistan have become very similar sides now - slightly old fashioned with 7 batsmen and 4 bowlers. South Africa definitely edge ahead with Steyn and Philander fit,and Rabada makes this attack relentless. Piedt can hold his own too but can be a bit one dimensional and on some conditions, I can see this attack blunted.
Pakistan probably have the most inexperienced and inconsistent attack among these teams, none of their bowlers are great with the new ball, other than Amir, none of the seamers can sustain pressure by cutting out boundary balls, and yet with an attack of Amir, Sohail, Wahab, Yasir, it's probably the most diverse and varied attack because all 4 bring something totally different and are wicket taking bowlers.
So, if consistency over a period of time is considered, then England would be my pick with their balanced 5 man attack with 3 extremely potent seamers.
Australia and South Africa both have one exceptional wicket taking strike bowler supported by very good seamers which edge give them the relentless tick in their own conditions. If a range of conditions is the key, Pakistan probably edge ahead.