Old car or new?

This is totally dependent on your mentality. And of course, there is a price differential. So, it is better that you identify your needs first and then take a call on the one that suits your purposes.
For instance, if you are someone who is looking for a regular upgrade in say, every two-three years, then a second-hand car makes sense. Moreover, if this is your first car and you are trying to learn driving on it, a second-hand car definitely makes much more sense. On the other hand, if you are someone who is happy using the same vehicle for a number of years, then a new car is definitely recommended.
Of course, there are other important parameters like your negotiating skills and the previous owner. For instance, a Parsi owned car commands higher value as Parsis are known to maintain their cars very well. As a Parsi friend confesses, We do not believe in repair? we replace.? Whereas even the latest model in the hands of a Young Turk (a la Schumacher) would create imageries of burning tyres and engine on an overdrive.
Before buying any car, here are a few things you need to consider:
1. What is your budget for the car?
2. What is your monthly budget for the car?
3. How do you intend to use it? Within the city or even outside the city? (Heavy weight age towards the latter means that you need a MUV or multi-utility vehicle like Tata Sumo, Mahindra Bolero etc.)
4. How long do you intend to keep the vehicle? Now that you have answered the above, you know whether you want a new or an old car. But before you go for that old car, get yourself a cool car mechanic that is, a trustworthy one who will check the car for you. Ask him to check all the parameters like tyres, suspension, cooling etc.