Megabus is great if you are looking to go somewhere cheep and fast. Every time I take Megabus, they are on time and loading and unloading is really fast and efficient since time is money for them of course.
The seats are comfortable with good leg room with exception for the front window seats on the upper floor of the double decker. The free WiFi is reliable on most coaches.
Don't be late for your bus or you will need to pay again for a ticket to get on another bus.
If there is a stop to let people off or to pick up new passengers and you need to get off to have a cigarette or stretch your legs, don't let the bus out of your sight. It wont wait for you.