First of all, it will be quite informative if you guys first browse the previous related forums as the same things are repeated again and again.
Now coming to yur question,
Comparing santro and cultus, the good things about santro exec are:
Very advanced engine, very ecnomical and at the same time very powerful, much more comfortable as it has Mc-pherson suspension, the same that civic and corolla does, very attractive design, beautiful interior.
The advantages of cultus are:
Cheaper parts, higher resale value, lower operational costs.
But if you wanna go one step ahead of the santro, go for a chevrolet exclusive LS, it has everything that a santro does and the plus point that it's foreign assembled, has a 2 years warranty, much much stronger and safer than a santro, more economical than santro as it has a 0.8 litre engine and if you are thinking about the power than you have to drive it to believe it. The 1.0 litre version will also arrive shortly. And it is designed by italdesign labs, the same that designs ferrari. For more information on the chevy and the awards it has won, go to mymatiz.com as it was known as daewoo matiz before chevrolet bought the plant.