Buses from Shad Thames to Liverpool Street

Hi! Just moved in London (Shad Thames) and will be working in the City (near Liverpool Street). I've noticed a couple of buses going to Liverpool Street (47, 188 and 381? will take bus opposite St Saviours Dock). I haven't had time to test the journey. How long should it take me to get to the office, taking into account traffic on Tower Bridge? Which bus is the most reliable? How about walking to Liverpool Street (it took me 20 mins between home and Tower Hill, normal pace)?
Thanks for any input and tips!

Buses 42 & 78 go to Liv St. from Tower Bridge Rd. However, I highly recommend you walk it as it won't take much longer on foot than on bus. I reckon 35 mins. Plus you save money, plus you get some exercise, plus you're not stressing for the next bus to show up or get through traffic. As long as you leave home on time...