No idea about the Witz.
But i have a Passo 2012 and i can compare it with my friends vitz 2010 for you. We bought them almost at the same time.
Fuel average= 14-20km/lit (14 is the minimum, with Eco off and harsh driving)
Maintenance= Almost as same as Vitz, original parts however are expensive of all these cars.
Performance= Almost similar as they have the same Engine (1 KR FE). Although i have an advantage as my car is newer nd is of less mileage,
Fuel Average= 9-12 km/Ltr
Verdict= Passo is cheaper but Vitz is better looking. And fuel consumption is better in a passo
Word of Advise: PLEASE DON'T BE TEMPTED BY THE ECO MODE. Its not like the car will be running on water. Eco mode only lessens the amount of fuel supple to the engine nd ensures a steady flow. Its crap and burdens the car engine.
I drive with Eco mode off and the fuel average stated above is with eco off.
I hope this helps
Only rumour i have heard is that the new Vitz is underpowered with the 1000cc engine. Which may be true as the new Yaris shape launched comes in 1500cc versions.
But then again there are experts here and this is all my opinion