I agree, of all the area I have had, WWII US is what I like best, although I do have a really nice matching P-38 AC 43 with an excellent 43 holster. I'll hang on to it until I find a US piece I can't live without.
I dont have a collection yet...not for a lack of wanting one though. I like US WWII - Early Vietnam era weapons the M1/Garand/Carbine/14 rifles and 1911/A1s have piqued my interest since those were the weapons that fought the axis and took great measures to ensure the freedoms that we enjoy today
I like mostly old military bolt actions. I would say Mauser exclusively but dang it there is just something about those Mosin Nagant Russian rifles! So tough, reliable, simple, durable, accurate--enough, and just a little bit of ugly thrown in. Hard hitting caliber too! I love AK's too. About to get a chrome AK on consignment and I may just keep it. I sold it to a woman during the Obama craziness and I don't believe she ever shot it besides test firing with me behind my shop.
Anyway, I guess my favorite guns to collect are guns with history behind them. When I hold them I just think "boy if this could just talk!". I even like cleaning out cosmoline!
I collect the 1890/WWl/WWll American and foreign military weapons. The favorites in my collection are: Colt Model 1901 US Army .38 cal revolver manufactured in 1901, M1 Garand 1942, M1 Carbine and the Mosin Nagant 91/30, M39 and M44.