I like the sound of TDK SA-X better than the Maxell XLII-S. But either is CAPABLE of producing good sound. My biggest gripe with the XLII-S is the crumby rollers and/or shells that are currently being used. They are noisy and roll erratically. The XLII-S cassettes have gotten incredibly inexpensive compared to the days when they were made 100% in Japan. They can be bought for $.60 each in bulk from cheapbatteries.com. These particular XLII-S cassettes are made in England. Maybe they are cheap because the quality is poor.
On my Nakamichi ZX-7, one can manually adjust the bias, level, and azimuth for each individual tape. The SA-X is biased with a lower reading than the XLII-S (5 points lower on the Nakamichi meter) which causes the SA-X to have a brighter, crisper sound. I have a large supply of NOS SA-X tapes which are superb. I have not tested the currently available crop of SA-X tapes. There are some 60 minute ones available from the above cited source. I also have not tested the currently available crop of XLII tapes, but since they cost more than the XLII-S, which is contrary to what one would expect, my guess is that the XLII tapes are superior because of the lower quality of the XLII-S roller mechanism.
It is also possible that I got a bad batch, but other tapers I know have also been unimpressed with the XLII-S roller mechanism even though the tape is USUALLY okay. I have found the XLII-S tape has dropout problems (where the tape sort of skips or drops out), especially in the first two or three minutes of the tape.
Unless you know your deck has been calibrated SPECIFICALLY for SA-X, or unless your tape deck allows you to calibrate for each individual tape, I would suggest getting Maxell XLII, TDK SA, BASF (Emtec) CE, or Maxell MS since these tapes are all set with bias and level that are very nearly the same. In my experience, the SA-X is alone in having a significantly different bias and a slightly different level.
Good luck. I still love the sound of tapes more than CDs, if recorded off of a good turntable.