I'll probably still be on my classic A1200 running 3.x, though I might have moved from 3.1 to 3.5 or 3.9 and I'll probably have managed to grab an accelerator for it. I haven't really any plans as of yet to use 4.x or a derivative.
Reason being that I'm really in the whole Amiga scene for the classic Amiga, its aesthetic, and its uses (early 90s games, DPaint, and quite possibly one of the best OSes ever especially given its age =P), and don't have any plans to move to modern AmigaOS-based systems right now. Truth be told, I don't really need such things when I've got my IBM PC-compatible (lol archaic term) running Linux. (Feel free to point out reasons!)