(04 Dec 2016, 9:06 pm)Andreos1 wrote Kings Cross is your obvious bet.
If you are after buses...
If you turn left out of the main exit at KX and left again, you will end up alongside Regent's Canal. If you can get your angles and sun right... I've seen some laying over there too.
Other options that jump out are around Vauxhall and Canning Town. Lots of buses around there at interchange points and interesting background scenery too.
There's the bridges across the Thames - should provide some decent opportunities.
BTW. Glad you clarified the 'and back' part of your trip
Kings Cross will be first and last on the list of places to go with my train arriving and departing from here, from the I was thinking of going around Victoria, Covent Garden, Westminister/Buckingham Palace/The Mall, and may have trip down to Waterloo Bus Garage and Pimlico Bus Terminus as the are quite a few Borismasters to catch there. Other places which sprung to mind were Park Lane and Marble Arch, but I don't think I will have enough time to do them all despite being quite close to each other.
Basically after photos of the Borismasters, BYD E200's on the 507/521, Metrolines BYD1474 on the 98, Also looking for Go-Ahead's Scania Irizar EL1/EL2 and BYD's EB1/EB2 which have all been used on the 507/521. Looks as though EL1/EL2 are now on the 108, While I can't find any recent photos of EB1/EB2.