A simple twisted one.People have different preferences and these change over time. I currently like a 0.2mm steel wire, but have played with copper, aluminium and thicker gauges (though haven't yet ventured skinnier). How do you make/plan to make your armatures? A twisted armature will likely need different wire to a soldered one for example.
I've ordered some wire off Amazon so hopefully that will work, if not I will probably turn to paperclips.I have a couple of wires but I find they can be a bit too weak (as in, you can't get them into a bit of cork) so mostly I end up with not the best choice and that is Paper clips.. mostly cause I got tons of them to work through. much harder to twist and bend but not really hard