What oil to recommend is about as subjective as what wax to recommend.
I'm not running a diesel mind you, but I just swapped to Ford's full synthetic at my first oil change (7500km), not sure who makes it, but I was assured there were no issues with doing so.
If there is, Ford will be the ones dealing with it, seeing as it was the house brand, changed out by their technicians.
You'll get a lot of different opinions on the relative merits of each, why this brand sucks or why this brand is the best.
I'm no scientist, but I think if you stick to the well known name brands (Ford's in house brand, Amsoil, Royal Purple. Mobil 1 etc), you'll be OK.