I am having the same dilemma. Last weekend, test drove BOTH the Jazz Hybrid and the Prius C.
Still not sure which car to buy, will decide by the end of April the latest. So hard to choose as both has its pros and cons.

PROS
Jazz:
-Really light steering, straightforward CVT gear shift
-Spacious interior, "magic seats"
-IMA battery 5 years warranty, cheaper replacement ~RM7K
-Car can still go with dead battery.

Prius C:
-much more electronics (eg touch start, keyless entry, MFD etc)
-Save more $ on gas
-Continuous air cond when car is stopped.
-Currently #1 best selling hybrid in US & Japan
-HSD battery higher millage, better quality and built to last longer
-Full sized spare tyre

CONS
Jazz:
-Less gas saved on IMA hybrid system
-less electronics
-IMA battery more prone to failure (according to some news articles)
-no spare tyres, IMA battery located @ tyre bay, also noticed "cheap" white foam insulation surrounding IMA battery

Prius C:
-Only 3 years warranty on battery, and more expensive to change ~RM12K
-interior size, width and length is same as Jazz, except for height, which is 8 cm less.
-ancient gear shift box , no CVT
-stiffer steering and more abrupt braking
-need to tow the car if battery failure, cannot use petrol as back up.

Another CON for both:
-No option to upgrade to leather seats, I am really hesitant to install them outside for fears of quality/warranty.
-Although Prius C offers upgrade to the 2DIN multi media screen, its NOT the same one as used in the USA market. It doesn't have Entune software, which hooks to your phone for internet for Bing, internet radio, etc

FYI I read somewhere that during launching, Jazz was expected to sell 3000 cars a year in msia, and Prius C is ~4000.
Right now, in north america, Prius C sales are 6000 A MONTH  Although 2012 Jazz Hybrid skips the american market, they
will launch the 2013 Full EV Plug in Honda Fit