Well its personal, so here goes...

Holland and Holland - calibre choices .375FL Mag; .500/.450 or .500/.465; .577NE (possibly 2 3/4"?)
Purdey - calibre choices .369; .450/.400
Westley Richards D/L - calibre choices .450/.400; .450NE; .470NE; .500NE
Calibre choice is difficult and I would try to avoid overlaps in my personal collection, unless I were in the very fortunate position of owning multiples of each

So what is the rationale? Well the WR is not as expensive as the other two, but none the less a collectible classic and important development in DR making. This would be the rifle that I would actually use and would be in a suitable calibre for DG. While I would certainly want to shoot a H&H/Purdey DR, I couldn't see myself putting it in the cargo hold of a plane, especially if it was a rare classic piece. For this reason I'd be inclined towards the .375/.369 because I could shoot and hunt with it closer to home, particularly for driven shoots in Europe that I could drive to by car (or private charter plane

). However, I would just have to have a big rifle in my collection, so I might therefore go for the .369 Purdey as a driven boar rifle and a H&H in .577

If I were fortunate enough to come across a suitable collectable rising-bite Rigby sidelock from pre-WW2 (or for me preferably pre-WW1, just for personal interest) then I would add this to a collection without hesitation! Ideally it would be a .450NE or .470NE but could equally be in any of Rigby's other wonderful calibres or .303 especially in a sidelever. Also for that matter a pre-WW1 Purdey or H&H .303

Again its personal, and probably very much coloured by the fact that I'm British, but if were to chose a continental maker, it would either be an O/U double or more likely a Dreiling or break-open single shot. Clearly among the very best are Hartmann & Weiss and Peter Hofer, so assuming that I still had unlimited funds after my purchases above, then how about a Dreiling from one and a single shot from the other?

Why did I leave out Boss? No reason - other than with unlimited funds I would have a trio of O/U 28 bores by them!! Also I believe H&W use the boss system on some of their DRs so that could be an option. I haven't left out Peter Nelson, but I confess I don't know all that much about him. Still I will need someone to build my take -down mausers and falling blocks!!

As for engravers - that will take more dreaming.. err I mean research....