I recently used Safeway Tours for a return trip to Niagara Falls.
The cost is $20 return without a PAC card or $8 with a card. Once you arrive at the Niagara Falls Casino, they ask if you would like to sign up for the PAC card. It is free to sign up and means the next trip you take there is $8 instead of $20. Signing up to the card is simple, all you need is government Photo ID and they issue it on the spot. They don't force you to sign up if you don't want to, it's your choice :)
The service was great, it was on time and very punctual for both of my trips. Ensure you call at least the day prior to make a reservation. You are designated a return time for your bus ride back however can change the time if required and get put on 'standby' for a different bus.
I took the bus down, stayed 1 night and took the bus back the following day with no trouble at all. If you need to change your return bus time, you need to ensure you check in with the Safeway stand to specify which bus you would like to take and they will alter your ticket accordingly.
I'd highly recommend this service as its very affordable and easy, with lots of pick up locations.
Be sure to book ahead, have Government Photo ID and have your $20 cash ready and you'll be all good :)