Are hourglass shaped headtubes better that plain ones? Also if bottom and top tubes are joined together into a monocoque-like shape together with the headtube is it a good sign for strength and durability on the frame? The weld on my frame is 4cm long (the one that joins top and bottom tube.)
Hourglass shape versus traditional shape shouldn't make much of a strength difference if properly designed/welded. The headtube is pretty short overall so its pretty strong regardless of hourglass or traditional.
The hourglass shape often lends to lighter weight or an internal headset. Others are like that just for looks. I don't think it's much of a strength issue. As for the top and downtube being welded together, I believe it's one of those "6 to one, half-dozen to another situations". Both have been done many times, and many ways. with no clear winner.
