I have been using bookmyshow for few years. It allows you to book your tickets while you are sitting at home. No need to go to theater be in line for book.
What I most love about this website is they let you choose your seats. I can also see the theater seating arrangements.
They have divisions according to regions in Mumbai. So that you can choose best suitable theater, compare prices, see the availability of the show.
I have also used this website to book tickets for plays. Its a great time saver. Although they charge internet handling fee which is nominal. They also have different promotional offers for credit cards, debit cards and many more.
The bad part about the website which I do not like at all is there is no facility of cancelling booked ticket.
Overall it is a good website and user friendly.