I've been long time Amiga fanatic (classic) and Peg1 user for 2-3 years, but now also have been using OS4 with A1XE for some time. I'd say both OS4 and MOS are really nice systems, but somehow MOS seems to be more compatible with old Amiga software (at least than Final Update of OS4). OS4 has nice softreboot, which boots even faster than Pegasos
But there's one thing which makes OS4 impossible to be my main computer. It hasn't advanced in file handling area. Workbench has basically the same functionality than in 3.x... whereas MOS's Ambient has progressed more to DOpus Magellan direction. That wouldn't be that big flaw if there would be working Magellan or similar for OS4, but there isn't at the moment. Old 68k Magellan works on MOS, but not in OS4... and no sign yet of the promised new version. You have to rely on DOpus4 or similar, which is pretty clumsy nowadays. And I really think, that these kind of functions should be in OS itself nowadays.
USB support is MUCH better in MOS, thanks to Poseidon. And I also like MUI4 more than Reaction, but that's a matter of taste... anyway as a long term Amiga user, I feel more home with MUI than Reaction.
Prefs system is bit messy on OS4. The old way of having separate prefs programs for everything isn't quite capable of today's amount of options. It would need some evolution from the 20 year old system. I think MOS has also taken a step forward with this.
At the end, I still feel to be home with my A1200/060/everything most (typing this message with it now
, but Pegasos has taken a place as my main computer. OS4 at the moment is pretty much a nice toy for me. If there wouldn't be Pegasos, I guess OS4 would be entertainment machine for movies etc, but until there's better file handling possibilities, I guess A1200 would be mostly in use still
