I've been making butted maille out if 1.6mm stainless steel wire. Cutting the rings myself. This stuff is strong and heavy! It looks and feels great! The wire is a little pricey at 11quid per 30ms. I was still curious to hear what other materials people were using. What other gauges of wire ect. I've heard that weaker steel can stretch at the crown or on the shoulders and I'd like to avoid that.
I made a butted link hauberk some years ago out of galvanized steel wire (the stuff I got was used in repairing fences - 20 gauge). Not as shiny as other materials but I felt it was more authentic looking. It is fairly easy to form and cut. The mandrel I used to form the links was 3/8" diameter.
When completed there were some 40,000 links in it and it weighs around 40 pounds. I wore it over a gambeson I also made. The hauberk comes to about the groin (worn with a belt to adjust the weight somewhat) and to a few inches above the elbow (I'm 5'10").
I wore it numerous times to SCA type events and reenactments but never did much mock combat with it. I never had an issue with links stretching or popping out.
I will reiterate @catija's referral to the Ring Lord website. I have actually purchased chain mail supplies from them (for jewelry, not actual armor) and they have a great variety of materials, and quite a bit of information about working with those materials as well.
If you poke around their site, you will find lots of finished projects, and free resources. And, because they sell the loops, most everything will be labelled with the size of the loop and the wire dimensions. It should give you a good idea of the good materials that offer a good balance between wearability (i.e. weight and fluidity) and still offer some protection.