I will go for the Omas...

I am only acquainted with three pens on your list--MB, Omas and Montegrappa. Of the three brands, Omas has the best nib experience. If you have large hands, you are likely also to find the Paragon (the new model) a good fit. I have the Arco Paragon in F nib and it is the best pen I ever own, though it can get a little heavy after a while. But the large ink capacity just begs for it to be used over and over again, which is the ultimate reason of existence of any fountain pen!

On Montegrappa, they can be fussy pens so if you don't want to be troubled by them, stay away. I have the new Extra1930; and while the craftsmanship of the pen's exterior is impeccable, the nib is too stiff (like a MB) and the feed is only partial to Waterman inks...

If you like flex, I think you will find the Paragon the Paragon of a pen.