At some point electric is going to be the only real way forward (unless another power form appears). But currently electric still lacks to match what a conventional diesel can do, and until then it will not be the primary source in my view. I heavily disagree regarding trolleybuses and the in motion charging, the only locations where they can be considered a viable option is in cities which still have existing tram infrastructure, otherwise they're far too expensive and ghastly.
Personally i think that diesel will be the primary form of traction for quite a while yet, i also don't think we'll move straight to electric. What i think will happen is the industry will go through a transition period (i'd say it's already started) where Diesel-Electric Hybrid will increase in popularity and become the main player, as electric technology progresses with batteries becoming more reliable, have longer live spans and giving additional range. Then they could become the primary source.
From personal experience the Hydrogen-Electric vehicles such as the Vanhool A330s in Aberdeen and London are the way forward, they can match up to what a diesel bus can do and to me seem the "better" option. The only downside is poor reliability and initial costs, although i think the new generation of Hydrogen vehicles coming on the market will be more reliable. It will be interesting to see what the new Wright Streetdeck FCEV's which are being introduced with First Aberdeen soon will be like.
In short:
Diesel will be here for some time to come and remain the primary form of power.
Hybrid will most likely act as a transition to electric and nothing more. Hybrid vehicles are said to be cheaper to run, but in reality that's not true!
In motion charging/Trolley Buses have no real market in the UK and require far too much infrastructure.
Hydrogen is the closest to matching what a diesel/Hybrid can do and in my view the best of the lot, but can be unreliable and is slightly more expensive than electric.
Battery Electric will most likely be the future, but it can't match what diesel/hybrid/hydrogen can do in range. And a battery electric vehicle cannot last a full 18 hours in service, having charging stations at either end of the route would likely solve that issue but also increase fleet PVRs.