I have not compared the results of the sanding. Both SiaAir and Abralon seem to do an equally good job. SiaAir seem to last longer and have generally been less expensive to buy. Also, until recently SiaAir had some grit levels that were not available from Abralon: P1500 and P3000 notably. I believe you can now get these in Abralon pads. Oh, and SiAir are also available in 5" circles, as well as Abralon's 6" circle. Both can be used with or without CABs.
As my supply of Abralon dwindles, I have generally been replacing them with SiaAir pads.
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"None are so blind as those who will not see."