Plumbing – Is this copper piping

The safest way to bend a copper pipe is to use a pipe bending spring. They come in sizes to fit the diameter your pipe so you'll need two - one for each type of pipe. The spring stops the pipe kinking by supplying support to the inner part of the bend.

Simply slide the spring up the pipe, bend it and then work the spring out.

In general, yes, stainless steel is more corrosion resistant than copper. It forms a tightly bonded oxide coating which tends to prevent further corrosion.

If replumbing a house where copper pipes corroded (this is more prone to happen in some areas than others due to water chemistry differences) my first instinct at this point would be to use PEX plastic tubing, but for metallic piping I would choose stainless steel over copper even if the price was the same.

If on a water supply that is treated with chlorine, or which has salts, there is a slight possibility of a stainless-steel specific problem (chloride corrosion). Certain grades of stainless (316, 316L) are more resistant to this form of corrosion than other grades of stainless, so precisely which stainless piping you are being offered will matter.

Still, I'd choose PEX by preference - should cost less, and it's not going to corrode.