My Lego buses are just only fit for Speed Champions sets or some large scale City sets only. They cannot be combined with usual town vehicles and road plates. I think 8w bus is more suitable for combining with usual town vehicles and road plates. But some Lego parts are too large for 8w bus such as indicator light (Plate, round 1x1). So, 10w bus is my final decision.
The scale of my Lego buses is about 1:31.25 (4 studs = 1 metre)