I've done both..lochaber 2012 and Edinburgh this year. Lochaber was my first ever marathon so got a soft spot for that one!
To compare them: lochaber has a much smaller field and is nice and maybe more personal.
Edinburgh has bigger support on the course.. in lochaber you will see a few people in every lay-by but they were very encouraging!
In lochaber at the end there is a nice spread with tea/coffee and filled rolls. And if you have driven there in the morning you only have about 100m to walk to start your journey home... at Edinburgh you have a mile or 2 walk back to the park and ride buses which then take ages to get going and then ages to get back to where your car is!