There is one disadvantage on the round tube. The round tube usually has straps that straddle the stock subframe and that is your attachment points to weld where the 2" wide square tube can be welded along the entire length where it meets the subframe. Some manufacturers will use the straps on the square tube connectors to keep cost down so they dont have to bend it to follow the contour of the subframe. I have a set of 1" x 2" x .120 wall subframe connectors available if you are interested.
Jeff