best cartridge under $500

can i use a MM or a MC with a jolida jd-9?
do i even need to use a jolida jd-9 with a mcintoch c-30?

The Jolida can be set to accept either MM or MC. The C30 has a moving magnet phono stage. If you're going to use a moving magnet cartridge and like the sound of the C30's phono stage better than the Jolida, or if you just like the convenience of not having an extra box in the system, then you don't need the JD9.

Never having been a VPI or SME owner, I don't have a recommendation for you in terms of cartridge choice. In general, I've preferred moving magnets to moving coils and tend to stick to the cheaper end. At present, I'm using a $39 Audio Technica CN5625AL on my Linn LP12/Ittok rig, and am getting lively, engaging sound. The .7 mil conical tip is tracking at 2.25 grams and deals nicely with all my records, including some rather beat-up, bargain-bin albums. I've also liked the Shure M97xE mentioned above; its stabilizer brush really helps handle warped records, and the slightly shelved down upper frequencies make for pleasant long-term listening, never bright or fatiguing.

Moving iron and induced magnet designs are usually considered subsets of the moving magnet category as they typically have similar output and are attached to the moving magnet input on your preamp or receiver. The difference is that magnets are fixed in place and a piece of iron moves in the magnetic field to produce the signal rather than moving a tiny magnet.

Only you can decide what the JD9 buys you. Do you like the flexibility of using either moving coil or moving magnet cartridges? Does the JD9 offer a performance enhancement over the C30 that you don't want to give up? Yes, you might have to adjust the JD9 to work best with whatever cartridge you use with it. It's also possible that the C30's phono stage will simply sound better to you.