Mcintosh 275's or Marantz Model 9's What would you

the 9's, if excellent to mint...very rare, and arguably the greatest tube monos of all time. pair with a 7 and you're so 'there', its not funny.

These are very different sounding amps. Both are classic designs. Both have been "reissued" in modern iterations. If these are originals, the Marantz may have the higher market value if in excellent condition and unmodified. (But if originals, both will have very aging components.)

As to sonics, the Marantz with its EL34 output tubes has that marvelous EL34 midrange magic; the Mac trades some of the midrange magic for more impact/punch in the mid-bass. Read any comparision of EL34 tubes to 6550/KT88 tubes and you'll have a quick summary of the difference in flavors as between these two amplifiers. If you have high efficiency speakers, the switchable circuit in the Marantz allows you to move it's higher power pentode operation to triode operation which will deliver detail, delicacy and harmonic timbre that is hard to match in any amplifier.
.

rushton nails it.

Marantz 2's are even better than Marantz 9's in many peoples minds but only 40 watts. A pair of 9's are really only a tad better than a pair of 8B's but all of them are very good. Bob