I went with
zinc plated steel for mine. Got the parts from summit.
If you plan to get a shop to flare the pipe, talk to them about what you can use. I really wanted to use stainless for mine, but flaring was too much of an issue without very high quality tool.
I flared mine myself with a cheapish tool. Haven't charged it yet so don't know how well it's worked but flares look ok.
Don't forget to check with engineer for clip spacing.