At one time I thought stainless steel was good, but that was before finding the "easy bend" Copper Nickel alloy brake line. The CuNi line is about as corrosion resistant if not more so than stainless steel, and it is a dream to flare and bend.
Stainless on the other hand is very difficult to flare and bend, you need very good tools to flare it well or you can fight with the cheaper ones and get by (I've done both). To bend stainless you need to get it just right, it is very rigid, the bends need to be in the right place and just the right angle to get the line to fit. Softer line has a little give and can be tweaked by hand for a perfect fit, not so easy to do with stainless.
If you're buying ready made lines and they actually fit then stainless would be just fine. If you're making your own the CuNi is the only way to go, same for fuel lines.
CuNi can be bought at most autoparts stores these days (couldn't a year or two ago). Try part number CNC325 for a 25' coil of 3/16" copper nickel alloy line. They have other sizes and lengths too.
http://www.autozone.com/autozone/parts/_/N-5yc1s?itemIdentifier=73293more info from one of the manufacturers
http://www.agscompany.com/automotive/11list of sizes
http://www.agscompany.com/automotive/brake-fuel-transmission-lines/nicoppGrigg
