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

Didn't answer your question, did they. The housing construction is superior on the Maxell as is the tape structure. TDK is decent enough but will throw oxides onto the heads more readily.

Also, if you want to do this right have a tech internally tweak the machine for the exact tape formulation you choose and then run it without dolby. You will have some tape hiss but the trade off will be more dynamics, better detail and no phase shift. Good luck and don't listen to the nay sayers.

Maxell XL II-S is extreme for all but the very best machines such as the upper end Naks. You might just stick with XL II only as the performance return might be minimal.

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.