I'm quite familiar with the OS systems of all the top arrangers. Each has its weaknesses and strengths. I think Korg is easiest, not because I have one but because of the ease of quickly accessing things.
I did enjoy the Roland system quite a bit, but didn't like having all the external files in one big folder. Great that Roland does a great job guessing at the chords in midi files, and the Makeup tools and such was very nice.
Technics has totally changed from its earlier system and is much easier and better now, but they sure do some things "funny".
I've never been a fan of Yamaha's OS, although I know it inside out. Too much stuff is just not done logically. I do appreciate the ease of accessing external styles though.