I have carefully analysed the two cars.
Vitz is expensive due to certain reasons. It’s not that both cars have same engine so they are the same.
The most obvious difference is that Vitz has better resale and spare parts availability.
Now coming over to the technical differences;
1. Vitz has better and heavy suspension which is durable, comfortable and can support bigger rims and tyres with ease.
2. Vitz has better build quality; better quality plastics and better and heavy metal chassis.
3. Vitz has a better AC compressor which is the same as that of corolla, it chills more and doesn’t trip in summers under heavy load unlike that of passo.
Passo basically is a 660cc like car with bigger engine. It’s other internals are weak as compared to Vitz.
Rest if you are low on budget than passo is a solid choice.