best MM cartridge...

I third the AT150. I was lucky to find a nearly new AT155LC about a year ago and it ranks right up there with the best cartridges I've heard.

I went through a period of buying a LOT of vintage carts and then a LOT of low output MC carts that sell for up to $800.

In the end I kept only two, the AT155LC and the Denon DL103D.

The MC carts that I gave up were the ATOC9MLII, Shelter 501II, and the Benz Micro Glider L2. The Vintage carts were AT15Sa, AT500DR, ADL XLMIII, Grace F9E and others.

I also tried a Denon DL103R and a Rega Exact.

The two I kept were the best by far to my ears.

Good Luck

Since Raul listed B&O MMC2s moving iron cartridges, how about SoundSmith's modified B&Os?

Try a Dynavector DV20XH - a MC that can be used with a MM phono stage. I use one on my Rega P7 with the phono stage on my Rotel RC-1090 pre.

No one spoke about the Adikt?
However, sticking with what you have for a frame of reference is a good chunk of advice.
(A sub 300 dollar cart will usually sound better in a 800 table than a sub 300 dollar table with an 800 dollar cart.)

Dear Jlamb: Right now there is a rare opportunity, you can buy an almost impossible to find MM cartridge ( one of the best quality performer ever made ): Audio Technica ATML-170 OCC in NEW condition ( boxed ) through ebay Canada.
This cartridge do justice to your title thread.

Regards and enjoy the music.
Raul.