I used National express when i was working in London. The staff were all very helpful and efficient, nothing really! There always seemed to be something going wrong with my ticket or not enough seats for me on the bus. Sometimes you have to go to the station to check your booking, which can take time. Also if your train is delayed you sometimes don't get any information until you arrive at the station.
If you're looking for value for money then this is the place to go. I would recommend thisβ¦