best MM cartridge...

the at150 at around 300 bucks...

London Decca Super Gold - ~$1200 new, but you can move up the London Decca line to the Jubilee ~$2800 new, or the Reference ~$5200 new

The Clearaudio Virtuoso Wood ($800) is quite nice - believe it's recently been replaced by a new model at $1,000 - Maestro Wood, IIRC.

Shure V MR, if you can find one NOS, in original wrap. They are out there and generally go for $400. Rumor has it that with the come back of vinyl, Shure will put it back into production soon.

I have one and also a MC, Clearaudio Victory H. Its a tie.

I don't have any experience with the Ortofon 2M Black.

You're going to get wildly different recommendations unless you give us a price range and some other information about your system and what you like to listen to. If you haven't seen the forum below, you should check it out. It's long, but Raul has done his homework and he gives the reader a lot of good information.

Who needs a MM cartridge type when we have MC?