I’m not sure of the pros and cons, I’ve not used stainless as, I believe, it is brittle and breaks sooner at joins.
At least that is based on what we do here with glider/sailplane rudder cable, but they have tight ‘S’ curve fittings at the pedals, so might not apply to. A Q setup.

So tend to use galvanised.
The plans say which wire (size), I think it is referenced on the rudder disconnect snippet.