gas_man:-
It's six of one and half a dozen of the other, really. Yes, the engineer is more familiar with the nitty-gritty of the mechanics. However, the pilots have probably flown the aircraft on one or more sectors already, and will be familiar with how it looked on the last walkround, therefore being better placed to spot differences ("Hey - that tyre's wearing a bit fast - I wonder why?")
At an outstation, as well, the engineer may not be familiar at all with the particular aircraft, whereas little niggly "peculiarities" of a particular airframe will be reasonably well-known to the pilots in any medium-sized fleet.
All in all, it's not a bad idea for both to do a walk-round.