Depends, if you wanna keep your car for a while then go for Wagon R while if you want to upgrade in a year or so then go for cultus as it will sell on almost the same price.
If you are old orthodox mentality person then go for cultus, Wagon R otherwise.
If you think the shape of Wagon R is absolutely hideous and doesn't match with your personality then go for Cultus.
If you want fuel efficiency the go for Wagon R.
Cultus is a car from sparta, it will last you a long time for sure. Wagon R is relatively new vehicle but news are that its a very reliable car.
In the end whatever you buy, you wont regret it.