I thought that thinner walls have a greater tendency to kink or ripple. I use 4130 3/8x0.035 for most racks and 1/4x0.035 for small h-bar racks. Plus some 5/16 or 3/16 for inner splices. The 0.028 stuff is more expensive because of demand/supply I think, so I stick to 0.035. I've also used 304 to avoid plating.

I use the Ridgid benders. I found mine used a low prices. The bends are a little flat but they are generally okay.