Is there any reason you want the Instax Mini as opposed to the wide? The mini pictures are only the size of a credit card, which makes anything but close-ups hard to see. Compared to the Polaroid 300, the Instax 25 will be better as it has automatic exposure as opposed to the manual exposure of the 300.

The film for the One600 is not anywhere near as good as that for the Instax; Impossible has done some great things in bringing Polaroid-compatible integral film to market, but the sharpness and contrast is just not there yet.