Most of you guys already know that I really dig the Katana series.
My fandom started when I got a first-gen KTN-50 in a trade and decided to use it as a practice amp alongside my big-boy Peavey 6505+. I liked it more than I thought I would, but I found it a bit boxy and lacking features, so I quickly upgraded to a Mk.I KTN-100, which offered incredible bang-for-the-buck.
However, once I heard the original Artist combo in person, I knew it was worth the price of admission. So, I found a deal, traded up and got the Artist, which ended up replacing both the KTN-100 and my 6505+ half-stack.
Eventually, I sold the Artist for a small profit and picked up a Mk.II KTN-100 after realizing that Boss' second-gen updates really started to close the gap between these 2 models. The only thing I found lacking on the Mk.II KTN-100 compared to the original Artist was a slightly larger cab, the Waza speaker, and the front-facing controls, but the KTN-100 held its own tonally despite these differences.
If I was buying another Katana model today, a used Mk.II head would be my first choice, followed by the second-gen Artist combo (not the Artist head).
From what I understand, the brand new Artist head dumps the internal practice speaker of the regular head and most of the "extra" knob-controlled features on the Artist head can still be accessed and tweaked through the computer software on the regular head, making it less of a value. Thus, I think the Mk.II head is really the sweet spot, especially if you already have a cabinet of some type to pair it with.
The new KTN-50 "EX" and Artist heads are really just minor updates of existing products, signaling that the generation is probably nearing its end. I bet we see the first Mk.III Katanas hit the shelves in the next 12-24 months.