In between these two cars i will suggest Grand i10 unless you are a fan of German beauty.
I myself was looking at polo but due to lack of space and bad ASS
(which i heard from many VW owners) i changed my decision. Also maintenance will be slightly expensive for VW.
For petrol you can also think of Brio or Swift. Also if you have some time wait for new Jazz.
Grandi10 has more space, slightly better mileage, more powerful engine, better ASS
and more features than Polo.
Polo has better build, bigger boot and ride quality will be marginally better.
Still I would recommend you to have couple of more test drives and then arrive at a conclusion.