Recommendation for Cartridge for Technics SL-1200G?

The ART9 is a really good cart. For a comparison or simply to experience it, I would gladly arrange for you to try a Sensitive Sound ART Dark cartridge (which I import and distribute). It is a little lower in compliance and perfect for the SL1200G. No obligation...

I'm in Seattle.

If you're looking for ART-9 make sure you're buyin' from the official distributor (not from grey market dealer), so you can get factory retip in Japan for very reasonable price when you will need it. 

In general for Technics tonearm you have many cartridges to choose from brand new to vintage heritage. From MM/MI to MC. 

Just don't buy a low compliance cartridges and don't buy very high compliance. 

I would recommend the Victor X-1II (Beryllium/Shibata) or its cheaper alternative X-1IIe (Titanium/Elliptical). Both are great, the stylus on Beryllium cantilever is better. Any of them in NOS condition worth the investment. Even if you will buy an MC it is nice to have an MM alternative to compare one to another. 

On LOMC side the Dynavector DV-17DS with Diamond cantilever and Micro Ridge diamond is great, the mkII version is even better. 

I  recommend Shure's M44-7, 97xe(the latest version) or v15 type V.

I use a ZU Dl103 Cartridge which was on my previous TT on my SL1200G.  Best sound I have ever had from vinyl.