AT 33SA or OC9 for 1200 mk5

On Technics tonearm you’d better use MM cartridges with mid or high compliance with stock headshell. You can use MC, but try to avoid low compliance on this arm. It was made for MM cartridges and AT MM are great, don’t forget that you will have to re-tip MC cartridges, how can you do that ? Do you know the cost of re-tip at AT or elsewhere ? I’ve been using At ART2000 on my old Technics, nice cartridge, but i was blown away by AT-ML170 and AT-ML180 OCC MM series, they are more expensive than AT MC that you have mentioned.

One of the best cartridge for this tonearm is Stanton (and Pickering) from the golden era, upper model with Stereohedron styli, they are so sweet, i’m a big fan of them. They are not expensive and very nice for this tonearm/turntable. I have many different models, my favorite is CS100 WOS.

As you might know Kevin at KAB USA (who specialized in Technics service) always recommend Stanton/Pickering vintage models. In my opinion the lower models are nothing special, but top models are truly amazing. Read it and you will find AT-OC9 in this article too.

For MC cartridges you could change the arm for something better. 

Ultimately, your ears will determine what is "best"
I've used the OC9III. Great cart for the price, if your referring to that model, before the many iteration of new OC9  that were introduced last year. The OC9II is even little less$ and purportedly "better" than the III. Either way, for the price it's a good value.
https://www.lpgear.com/Merchant2/merchant.mvc?Screen=SRCH

I haven't heard/read anything on the newer OC9's. Likely all good, for their price point.

If you can up your game a few more, the ART9 is unquestionably a step above. Read the threads.I've used one off an on the past 5 years. Presently on my table.

Save your obsession/audio nervosa regarding compliance. Just get an AT whatever and enjoy the ride.

i would opt for the AT VM540 MM cart with your table. then sell the Phonomena, and look for a used Chinook. The VM540 cart is over looked because of its lower price. but its a musical cart, and mates extreeeemely well with your table and a chinook phono stage.