I find this quite frustrating because I can never decide who if anyone to talk to
After returning from the US, I initially found the system a little confusing to use, particularly in areas of service overlap. In America it is much simpler: (departure airport, flight following from one facility, destination airport).
I generally like to go for the best service available. This means, in decreasing order of preference:
1) Deconfliction Service. Not usually offered in VMC.
2) Traffic Service. Sometimes you get traffic with no "height" information - due to the other guy not squawking mode-C.
3) Basic Service, when you get that feeling that everyone around you isn't squawking mode-C.
4) London Info in areas not covered by LARS.
If there is CAS or an ATZ, I would either stay well away from its edges, or ask for a clearance to get to the other side. Better doing either of these two than to risk an infringement and get bo!!cked.
Other pilots may prefer not to talk to anyone.