I didn't really have the chance to watch Saqlain playing but he had a reputation of bowling a lot of tough overs including those at the death.
I watched a long part of Afridi's career and rarely did he bowl in powerplays or at the death. He almost always bowled his overs in the middle of the innings.
This isn't really a big deal - not many spinners bowl at the death anyway. However, there are many spinners with similar records to Afridi which is why he won't come into this discussion. Admittedly, he was often unplayable when he was 'in the zone', but like his batting, that was a rare occurrence.
I remember watching almost all (if not all) the games of Saqi .
1. Wasim used him as a surprise element in 96 WC v SA, when they introduced Paul Adams. Saqi was too aggresive back then. I remember him having a nice c&b and a decent game (don't think it was debut)
2. I saw the earliest signs of an away going delivery when he had Sachin stumped in Singapore for a 100.
3. Moin Khan used to called it ulta. The doosra phenomenon started only when he got a fifer in Brisbane vs Aus in the tri series. Neither Aus nor WI could pick his balls.
4. He also got another fifer in the Sahara cup, which made Wasim say that he is the best spinner in the world and tipped him for 500 wickets.
Now the thing is I think Saqi got a lot of cheap wickets (taking nothing away from him) due to his doosra. Batsmen used to go for the slog and were out stumped or caught. Those were the days when teams used to go at 4 an over till 42 and then accelerate. Saqi usually bowled his last 4 from 42 to 50.
Very rarely have i seen him under pressure, but i did see him wilt under pressure once when Rajesh chauhan hit him for a 6 in Karachi. Saeed Anwar, the captain cried foul saying ball was changed and Saqi was not able to grip the newer ball thus enabling Chauhan to him him for a 6, which makes me wonder whether or not he would have succeeded in today's world of big bats, small grounds and bang bang.
I think Afridi's 'in the zone' bowling occurrences were far more than his batting. He has been unplayable at times (2011 WC comes to mind).
My only problem with slating Saqi as ATG spinner is the sample size. I don't think he played long enough and was tested enough. He had the first movers advantage with the doosra and rightly so, which fetched him heaps of wickets.