They all have the same cockpit so just depends if you want lighter and better/ faster runway and climb performance, then go 600 or 700.
If you want bigger, heavier needing quite a bit more runway and more sluggish climb at full loads, then go 800 or 900.
I have all 4 and rotate between the 700, 800 and 900 regularly. I save the 600 for when I want to fly from Las vegas to places in the desert that don’t exist
I’d have to say I think the 900 might be my favorite