I have used Ola cabs in Delhi & they always denied the booking on last minute, the charges are too high specially with the peak time surcharge.
Their App is also tooo slow, however I really like the concept of Ola auto which is quick & easy & the cherry on cake is the auto charges as per meter which is really good & cost effective. However I have also used Ola cab in Indore & they are absolutely brilliant & quick & hassle free, just 05 mins & your cab is at your doorstep which is tooo good & prices are also quiet good & not much expensive better than taking a auto.