I recently purchased Wagon R after considering many other options like Eon, Alto K10, Kwid. But the cabin space is much better in this car. 5 persons can easily accomodate inside it. Regarding performace 1000cc K10 engine delivers decent mileage of 17 kmpl in city and 20 kmpl on highways.
Car can easily touch top speed of 120 km per hour. Although it lags when A/c is on in low speed but what more you can expect from 1.0 litre engine.
Overall its a nice family car and will deliver its best Value for money. If your budget is under 5 lacs then go for this car. No other car will ensure the performane better than this.