The Kronos Pro is THE best table I have ever heard. I have a limited but it is essentially a Pro as I have the new fancy motors that are in the Pro. There is no question I would take the Sparta over a 20/3. I think the 0.5 Sparta would compete nicely against the 20/3 and of course then there's the lovely AMG Viella to consider. The big advantage of the 0.5 is the ability to upgrade to a full Sparta. The advantage of the AMG is a world class performance and the ability to accomodate a 12" arm within its small footprint. The Sparta maxes out with a 10.5 and SME is designed with 9" in mind. The Viella also has an option to run a second 9" arm something neither the Kronos or SME offer. The SME's downfall is its an SME which can be turned around to be seen as it's strength, hopefully you get what I mean!
The Sparta is my fav as the dual rotating platters, something I was really negative about until I heard it, really really works.
But man so hard to say anything negative about all these tables, such great choices out there these days. With all three the 0.5/ Viella/ 20/3 all sounding so good, maybe buy the one you like the look of best.
Sorry for the boring, too politically correct post!