I thought it depended on what type of brazing you're doing. Bike frames are often silver brazed so you'd need the oxygen boost with propane to get the concentrated heat (1200F) for the joint to flow right and quickly. I think bronze brazing might be less intensive. Most frame builders I think use oxy/acetylene for the precision and speed, so you minimize the impact to the tube's heat treatment. Depends, too, if you're doing lug-less fillets.
But lugs, dead sexy. Henry James, Richard Sachs, oh hell yeah.
My understanding of the brazing process is it takes a fair bit of practice to get it right on bike frames. If you use lugs, they are heavy, the tube walls thin and the solder temperamental so you can easily get too much (ruin the tube) or too little heat (bad joint). This is one reason why high volume frames and even custom frames now are TIG & MIG, a lot less black magic to attaining a good looking and safe connection.
But the hard part isn't even the joining of metals necessarily but fabricating a jig that lets you do it so the frame is straight enough and doesn't require much (ideally zero) cold working after to align. That is one advantage of lugs, they tend to be self aligning and all the tubes cuts are less critical. Fillet brazing and welding you'd need more tooling to cut the miters and hold the tubes. That is again why higher volume is lug-less, investment in the table or jig is one time and amortized over all the frames. For a one-of, lugs make sense.
Just a hint, you might want to talk to John Henley and Terry Holben. John is a wizard with artistic metal in general (and has made bike frames) and Terry has been threatening to build us all fat bikes for, like, ever. If we can get you two into a race maybe we'll finally start seeing some frames coming out.