I own 1942 and both expansions as well as Vietnam, and I'll have to say 1942 for now.
After Vietnam is patched it will be awesome and even 'as is' it's alot of fun, but the question is which one now, so I'll go with 1942 v1.6 with EoD mod based on smooth gameplay and features(which have strangely been left out of BFV's initial release).
I'd definately say 1942. I have nothing big against Vietnam, my opinion is based mostly on my own interest in history. Like Mihail, I really don't care much about the conflict in Vietnam.
Now that I have VietNam i like it better :) Listening to music is fun, espcially "Surfin' bird"