I was in your shoes some 3 years ago when I was looking for a Jazz. I had just sold my Landrover Freelander Auto and was looking for something a little more economical
I ended up with a 2010 I-shift, ex Honda company fleet. The car was superb, very well turned out and I was very pleased, except for one thing. The I-shift gearbox was in my opinion rubbish. It was neither a manual or auto gearbox, but something in-between, depending on it's mood! I know some drivers swear by it, saying they can play tunes on it? However I ended up swearing at it!
I subsequently moved on from that to a new 2011 CVT Auto. This is a different car altogether, very smooth with it's torque converter, in place of the electric clutch. and it's always in the right gear.
Just had it's 2nd service with currently about 14k on the clock and I won't be getting rid of it any time soon.
So, If you want a manual gearbox, then fine, but if you want an auto, then steer clear of the I-shift gearbox.
The Jazz is very much like a Tardis, has a vast amount of room inside and will return around 57mpg at 60mph on motorways and around 38-40 in town. I can certainly recommend it.
Regards