Trying vinyl, need some help!

For the last month, I have been searching for a good cd player or transport and thought I had settled on a Mcintosh unit when I started looking and turntables. I found a Roksan Radius 5 with a Nima tonearm that was in my budget so I bought it.
Now comes the problem, the cartridge. There are so many to choose from and they are not cheap so finding one that would compliment the table/arm is a bit intimidating.
My Audio Research preamp has 2 inputs for MM, or I can purchase a dedicated MC preamp.
If anyone has any experience with the Radius 5 please let me know what you have tried.
@ brianmoriarty No clue what the SP4 sounds like yet, I tested it for functionality as soon as it showed up and began tearing it down to clean and modify. Oh and I looked at the Grado Masters, I am leaning towards the Grado for now.

Thanks to all for your input, help, and opinions. It has helped narrow a large choice down to 30 to 40!
I'm basing my opinion of the SP4 on The Audio Critic's test in 1977 (Preamp Survey). I recommend you read this report! And I only paid $800 for my SP6 (in original factory box!).                              Regarding cartridges: any of the upper-tier Grados will do! I still have my vintage G1+ mounted in a headshell as a backup spare!
You said your budget was under $600. The last time I looked the Grado Master was $1000!
@donvito101 Ah yes you are right, but I found one with about 50 hours of use on it for $600, so it is also in range!
@ roberjerman I guess from a performance standpoint the moving coil IMO would be the better choice. Less mass to accelerate/decelerate would give the cleaner more accurate information, I know this isnt always true in practice but I guess the only way to find out is to buy a MC and MM at the same price point and see which one I enjoy more.