I own(ed) both.. still own the Genos..
Genos is the best arranger for people that want to play music straight out of the box, and enjoy playing covers as close to the original as possible.. its also fit for solo use on stage... the content it comes with is mostly aimed at music from last century, it can however be addapted in any way you want. It has one competitor the Korg PA4x, when we look at its main purpose, the Genos rules this cattegory and is worth every dime..
Montage is a workstation that challenges people to become creative, and create their own music. Its meant to be used as part of a studio, or on stage in a band.. the tools it offers are diverse and the content is more aimed at modern music. It has fierce competition. There also is the modx, which has basically the same sound engine as the montage, but fewer controlls and lower build quallity. Its competitors are the Roland Fantom and the Korg Kronos/Nautilus.
The fun thing is, the Korg PA4x holds the middle ground between Genos and Montage, and becomes an option for certain musicians that want more creative controll either live or in preperation above the Genos.
Anyway, you can’t go wrong with any of these two.. but carefully decide if you need a Montage, or that a modx suits you just as well.. keep in mind that both don’t have styles, if you want styles, go for the Genos, the arps in the montage can somewhat function liek styles, but just aren’t the real deal for most..
In the end, i personally would like yamaha to crossbread Genos and Montage, and to even add some features of the YC series..