No experience in riding the Megabus, but the stop where you get on is on the same block as our office (well for the next week, we're moving
)
There are times the lines are very long, if you did not know that. Like to the corner, around the corner, and down 33rd a bit.
So if you do it, leave some time to get there early so you aren't way in the back, and if it's cold out, dress warm, the wind kills you on that block.