If you want quick and comfortable, go with Amtrak. It's not even close.

Bolt/Mega are basically the same thing. If you go with a bus just take the cheaper option that works with your schedule.

You could also take NJ transit to Trenton and connect to Septa to downtown Philly. May take a little longer than the bus, depending on traffic but should be more reliable and comfortable. You also wont have to adhere to any set schedule since walk up fares dont differ from advance purchase fare.