best MM cartridge...

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?

03-09-08: Jlamb
...cheapo phono pre I picked at a TV repair shop for $25 new. I have an AR ES-1 on the way w/Linn Basik LVX arm and K9 cartridge.

I encourage you to sit still with the K9 and get to know it before you start a quest for the perfect cartridge. Live with it and get a frame of reference. It'll help you understand what you want.

In my opinion, the only thing you need right now is a better phono preamp. Whatever your $25 unit is, it can't be doing justice to any cartridge. Phono stages are often overlooked by folks just getting into vinyl. There's a tendency to think "that little black box can't be doing much, so I'm not gonna spend much on it." Some of us need to learn things the hard way. I know I did. Phono preamps make or break a cartridge. Avoid the stuff under $150 (NAD, Parasound, Musical Fidelity, Music Hall). Of course, you have to decide what you can afford, but if you can strecth to $500 for a used piece, I think you'll be surprised how good that K9 sounds. I'm a big fan of tubes. In my opinion, a few units that stand out in this price range are: Bottlehead Seduction, Pro-Ject Tube Box SE, AES (Cary) PH-1, Wright WPP100c and WPP200c.