#1 Lugged . . . and yes had a fully lugged tandem silver brazed. Longevity? Rode it for 64,000 miles.
#2 Fillet brazed . . . a nice clean seamless look, but without fancy lugwork.
#3 TIG welded . . . lumpy looking/le$$ but just as good as the others.
Beauty is in the eye of the beholder.
Here is a fully lugged (with wndow cutouts) BB shell on rear of our current tandem . . . in carbon fiber. Currently 22,000 miles on that tandem.