New Cartridge Suggestions

Thanks everyone for your recommendations.  Noramance, the George Warren tt came with stock Rega 250 with wiring mod’d by Moth Audio.

Has anyone had experience with the entry level ZYX carts?  There are 2 here. But, 1 is from outside the US & people seem to be leary of that.

I have been using a vintage Audio Technica AT15ss since 1975 when I purchased it new.  I had it mounted in my Marantz 6300 TT which was also purchased new at the time. 

About a year or so ago I picked up a used VPI Ares3 TT with the super platter option and found a used SME Series IV tone arm, which I mounted on a custom machined arm board I made.  

Everything I have ever read about the AT15ss and the AT20ss  states that they are two of the finest cartridges ever produced and both are identical other than the AT20ss' were the hand picked cream of production.  I always wanted the AT20ss stylus so that I could replace my AT15ss stylus with the finest one.  After moving the AT15ss over to the new to me Ares3, I was blown away at how much better it sounded in the new set up.  I mean it was like mind boggling. 
Everything good written about the AT15/20ss was clearly evident.  Luckily, I recently found a NOS in the original packaging, AT20ss stylus which I installed.  It's pretty much the same to me as the AT15ss, however I just feel great knowing it's in the system now.

If you can find yourself a NOS AT15ss or 20ss, buy it. You will not regret this purchase.

@tochsii Replace the Moth RB250 with a Jelco 850 (750 new old stock or 550 new if budget matters - 850 is well better.) from George Merrill and install any of the recommended cartridges for a major upgrade (mind-blowing) for relatively little money. The arm you have, while competent at the lower end, is a weak link. Honestly, you are overthinking the options. Forget the ZYX LOMC and use the Nag MP150 or Blue for starters with Jelco.