Sorry, I should add - each manufacturer has their way of doing things - the way the buttons are laid out, the way the voices and patterns are accessed, quick chords etc - and these are kept relatively consistent through their model range.
So one of the advantages you might find with Yamaha's huge coverage, is that if you started yourself on say a PSR-E333, you might find that if you then jumped onto a $3,000 PSR-S710, you might actually find you pick up the technicalities of it a bit quicker than if you were a dedicated Casio user.
The Y-man