I think the train is more cheaper than the buses . And the station are located nearly each other . It is asafe and the convenience for the travelling .
As per my experience buses and tube train is good option for travelling, that is really nice service in London, you can get good transport service without too long waiting. it is too fast and comfortable also and easy to get.
The buses are cheapest in the u.k . And the station of the buses are so close to every residence and the commercial area that every one can easily reach there . And the ticket are also low budget .