What types of metal do you use for your robot in general?

[MAXOFLIFE]

This year we constructed most of our robot using 1"x1" aluminum tubing. It worked, but we had numerous problems: warping from over tightened bolts, extra holes needed to help guide and tighten bolts, etc. I know every year can be different, but what types of metals (and in what shapes and forms) do you mainly use and for what reason? We know the basics: aluminum being lightweight, steel being strong; heavy; and prone to rusting, etc.

Thank you for taking time to help!