For most applications, the best tubing is mild steel,
1 5/8" diameter, .120 wall DOM, mil spec. DOM stands for Drawn Over Mandrel, which means the tubing is seamless. A welded seam significantly weakens tubing. ERW tubing is seamed, ERW stand for Extruded Rolled and Welded. Also mil spec DOM is certified for content and the diameter and thickness are held to extrmemely close tolerances.
Most often the 1 3/4" wall tubing sold by the majority of vendors is ERW, and it is .137" wall thickness. The reason it is that thick is because it is not mil spec certified, and the content and wall thickness are not as closely controlled.