[Dave L]

I have had square bars and round.

On the thule rack (square) accessories will be very secure and not rotate on the bar, the down side is that if your roof is curved the bars wont be parallel so if you are carrying wood or other flat stuff it wont make full contact with the bars.

Round is good on a curved roof but I had my ski rack push back in the wind and the universal mounts on the ski rack dug into the paint. I also find that the paint yakima uses sucks and it has flaked off the "new" ski rack and the brackets.

I brought home most of the materials when I finished my basement using a roof rack (including some 10foot sheets of drywall) and I regularly carry bikes, kayaks, skiis and snowboards.