I prefer the braze-on FD + clamp combo more because over time with FD adjustments, it damages the seat-tube less. Every time I have to slide a one-piece FD up and down or rotate it to fine-tune, it leaves a little clamp mark on the paint. This was especially apparent on one bike where I had fitted different front-chainrings for road-race versus TT use; after a couple of swaps, there was annoying marks above and below the clamp. With a 2-piece design, I place the clamp in the middle of the range I would move the FD. Then I just unbolt the FD and slide it up and down the clamp as needed without disturbing the frame. This is more distressing on a CF frame.