If the bus is slowing you down, pass the bus.
Keep in mind that it's usually illegal to pass a bus on the right as it approaches a bus stop or is stopped in the act of picking up or discharging passengers. You would only pass a bus on the right if it's in a thru lane and part of the traffic flow.
Passing and staying ahead of buses is my main form of competition during the commute.
RichC
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Training: 2002 Fuji Roubaix Pro (105 triple)
Commuting/Daytripping: 2001 Airborne Carpe Diem (Ultegra/XTR, touring wheels)
Commuting/Touring: 2000 Novara Randonee (Sora/Tiagra/LX, fenders, lights)