What is the “World’s Best Cartridge”?

Depends on your system and taste.

@lalitk 

you will not regret it. best wishes with your new analog rig.

the standard Etsuro Gold bettered my previous references clearly including the Clearaudio GFS, Anna Diamond, and vdH Master Signature, which were the most recent one's i had. i had many others over the years which that group had bettered.

i've also been very impressed with a field coil cartridge made in Lithuania, the DaVa Reference with a tubed power supply. i've had it for a couple of months and figuring it out. it does some amazing things too. 

Very interested to read this. I am a moving iron fan, and have a London Decca Jubilee and a Reference. When the Reference went for its final re-tip (the maker is retiring and it is uncertain whether anyone will be able to service these cartridges in future), I decided that rather than just use the Jubilee, I would explore other takes on the MI principle. I bought the little brother of the Epoch 3, the Statement 3, and bore with it for 80 hours. It's a good pickup, but it doesn't excite me the way a Decca does. There's something about not having a cantilever, and taking the signal immediately above the stylus from the Decca's armature that gets the timing just right. I guess it's like comparing a CD player with uncorrected jitter against one that has none (if only!) However, there is a design very similar to the Grado that does an amazing job for less than a third of the price - a Nagaoka MP-500. It is very, very close to the sound of a Decca. And while it is a (relatively) cheap pickup, it ended up costing me - I bought a second SME turntable to make a permanent home for it so I can be more sparing in my use of the Reference when it comes back. If it cannot be serviced again in the future I have to stretch its life out as long as possible. I spent some time swapping cartridges and comparing the above mentioned, and also the Benz Ruby 3 I was using before the Deccas came along, its predecessor the Wood H2, and an Ortofon Kontrapunkt C. I have a clear ranking in my mind about which is best, for me, and so on to the least pleasing. None of these are in the OP's league, but there is hope for us mortals! BTW, I have never had any tracking issues with the Deccas with a damped SME Series V arm.

mglik, Keep in mind that when you "heard" the $25K cartridge, every other piece of gear in that system, which I take it was new to you, was also different from your own rig, not to mention the room itself. Therefore, it is folly to attribute the final result to the cartridge alone. That’s what makes this pursuit so endless. Put that same cartridge in your own system, and you may feel it’s not any better than what you have, which is already top drawer.

Dogberry, You do realize that the Nagaoka MP500 is a MM cartridge, not an MI, and therefore not much like any Grado or Decca, except perhaps in its SQ, which I agree is excellent.  The dirty little secret of cartridges is that excellence is not always proportional to cost.

From long ago experience (1978) a Grado Signature Two ($500) on a Denon TT/DA307 arm  sounded particularly fine! YMMV!