I have a Shelter 501 MII and to me it sounds better than my old Vandenhull Frog.
Here is a cool site you will like. Discussed are the best cartridges, including the Shelter 501 MII , Shelter 901,
Lyra Helikon, Vandenhull grasshopper, ZYX R-100 Fuji and many more.
This is a must read,it should answer a lot of questions for you, detailed and thorough, I hope it will help you.
http://www.high-endaudio.com/RC-Cartridges.
Be sure to check out this whole site especially reviewing the reviewers.
Good luck, and very good listening.
Let us know what you finally purchase.
Ron