Yamaha is the best operating system for an arranger. The SMF playback of older GS ( roland) files is inconsistant, but your question was easiest ARRANGER, right?
No contest - the yamaha is the easiest to get around with. Style buttons, mixer funtions, voices that don;t cut off when you change voices etc....
The G1000 is a deep instrument, but not the easiect to navigate. The Keytron stuff is a close second, and then there's Roland, Korg and Technics tied for third in my book.

No ONE intrument has all the bases covered, but Yamaha comes closest in ease of use and above average sounds.