Redbus.in is one of the best online ticket booking portal for buses. I frequently travel from pune to kolhapur and vice versa. I always go with this site for booking, they always give you offers on tickets which is worth to travel. redbus seats are comfortable which matters alot .
In case you are late to reach at pick up point they will wait and give a call, so they are good at service and support.
redbus app is simple to book a ticket and this will not takes a time to load . so u can say its a user friendly.