TDK SA-X or Maxell XLII-S which is best?

Maxell is the stronger tape, TDK sounds better BUT!!!

This is assuming you have adjustable bias, consult the bias setting in your manual if the only bias controls you have is normal, High and Metal. The manual may have the answer to your question on which tape will be best for your machine.

Atleast I know I can rememebr things from 15 years ago.

It depends on which tape your player best matches regarding bias and EQ. Either is a very good tape.

A couple people did a very good job at addressing your question already, but I'd like to add that the "best" tape can be deck dependant. The calibration of a deck can favor one tape over the other, this was alluded to above.

Celtic66 is on the mark.

I strongly second his advice to have the deck calibrated. This is typically done to max out performance with a specific brand / type of tape.

I also strongly second the advice about losing the Dolby.

A good metal tape run without dolby on a top cassette deck that has been professionally re-calibrated can come surprisingly close to the sound of the source.

Analogique in NYC does this type of work and it is not expensive.

Why don't you buy one of each and do a test???