If you intend the arranger as merely a “scratchpad“ for working on the songs, and you intend to finish them in the computer later, to be honest the overall sound quality of the arranger doesn’t matter all that much. In all probability you will be replacing out the arranger’s sounds with better computer-based sounds like drum kits, percussion, piano, strings etc. using the arrangers midi output.

So all in all, what it ‘sounds’ like isn’t that big a priority. However, the ease of either creating your own styles, or the availability of a huge selection of already created styles may very well be a high priority. In this area, Yamaha have a huge advantage over Casio.

Just something to consider…