I am in London right now. Just finished our second day using the Big Bus hoho. They sold us the two day ticket for same price as one day so we took it.
Don't do it.
Horrible long waits, buses take forever to get anywhere. If bus is crowded( in season it is !) you may end up standing, we did twice, and can't plug into commentary.
Take regular buses, we did at first part of our trip( we started in London 27 days ago, toured some other countries and now are back for a few days before we fly home).
A rrcel card is less then 9 GBP a day and you can hop off and on all day with that ticker. Regular buses come every 3-5 minutes , not so with Big Bus.
Would not recommend hohos on London, although I would for Paris.