I would suggest you to go for the Jazz, as many guys have already suggested here.
Here are few points to go for Jazz:
1. In terms of fuel and your daily run (< 100) you won't be able to recover the Diesel car price compared to petrol in a long run (but only after 5-6 years). Someone in previous post has already calculated this.
2. A Petrol car's maintenance will be cheaper than a Diesel car with long life.
3. Overall space in Jazz is much more than Swift (the boot & rear leg space), also the interiors are very decent compared to Swift. Swift is more cramped from inside than it looks from outside, comparing with Jazz.
4. There won't be any difference in Diesel & Petrol prices in near future as govt. will end up giving subsidy for Diesel.
5. Option of CNG with petrol engine, someone pointed this previously.
6. Dealership and service centers are lesser than Maruti but are adequate to serve you.