wow...surprised no one touch this one yet!
If you are inquiring about cab vs coupe because you're on the fence, here are my thoughts in deciding the same question.
One cannot beat the utility of the cabrio. Closed, it keeps you high and dry, part way open, it gives you some of the utility of the panoramic sunroof, and of course, then there's the full blown, rails off, windows down, let it all hang out full blown 'vert feel (of course, which I haven't experienced...yet!

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Main cons with the cabrio would include noise , thermal insulation and durability. The road noise doesn't seem too severe (....I don't plan to use the car zooming around in the 70 -80 mph range much), and thermal insulation can't be too worst then having the big panel of polycarbonate over head. (The Pure hardtop would gain this advantage). Durability always is a negative , I don't care who makes it - metal always holds up better then fabric! However I didn't see too many complaints in the 450 model, and surely the 451 cabrio top must be better.
Other factors- appearance! quite often the softtop has a "negative" appearance over the hardtop.....it usually spoils the lines of the car. But in the fortwo's case because of the roof rails, the 'vert has very much the same appearance - it does not detract from its appearance. I also think the fact that the panoramic roof on the coupe does not open helped my decision. A working sunroof might have tipped the scales back to the coupe...although I do already have one of those in my MINI anyway. So I'm looking forward to our smarts summer arrival, putting on the sunglasses and dropping the top!