Walther had the most wartime production numbers in total...here is an excellent link to some production info, via the P 38 forum. Certainly collect ability is linked to lots of things with the pistol, including all numbers matching, bring back or import, correct grips, magazines, etc. I started getting into the P38s last year...you can't beat the expert info you get from the p38 forum.
http://www.p38forum.com/P38ProductionDates.pdf