Iron, chrome and aluminum. The different letters are just different ratios.
If I could find KD core wire I'd use it but just because it colors well.
All the alloys taste the same to me so the only reason I use different ones is for the color. Occasionally I'll try to hit a certain load so I'll use different stuff but I mostly use A1 because it has the most resistance and I'll throw a few ply of n80 in for some stripes or something.
When I get more
batteries for my my quad parallel I'll be seeking a lower load but I'll still be using mostly A1. Just more of it with less wraps.