As far as the bending of pipes is concerned, both grades of steel can be curved equally well. The differences derive from the applications for each grade.
A53 is pressure tested for liquid and gas flow so is best suited for those applications. A500 is not pressure tested, but is suitable for structural applications where nothing is to be conveyed through the pipe.
A53 most often has a lacquer finish on the outside which is fine for liquid and gas flow but not desirable in most structural applications. A500 is bare except perhaps for a fine oil coating to protect it from rust before it is cleaned and painted in a structural application.
For structural applications, A500 is better in that custom lengths can be ordered from 20 to 75 feet (varies by size). A500 also has closer O.D., wall and straightness tolerances.
Lastly, because A53 has been certified for pressure applications, it costs more. A sample of one size indicated about a 5% cost premium over A500. Of course there is no need to pay that premium if hydrostatic testing is not required.
