Aluminum
Lightweight, non-tarnishing and budget friendly. It is able to be anodized in many bright, shiny colors. Wash with soap and water.

Jewelry Brass
Strong and fairly heavy. Jewelry Brass will tarnish pretty quickly but can be cleaned with any jewelry cleaner safe for brass or copper. I use this mostly in my Steampunk pieces where I plan for the patina to add to the piece.

Stainless Steel
Fairly strong and weighty, will not tarnish. There is nickel in stainless steel, but it is bonded at the molecular level, so does not react for people with metal sensitivities. Wash with soap and water.

Sterling Silver
Shiny and pretty! Has a medium weight, a silky feel, but also a larger price tag. Most people with metal allergies are able to wear sterling, but some highly sensative individuals may still react depending on the alloy. I work with .925 Sterling Silver, Argentium Silver and .999 Fine Silver. Clean with a silver jewelry cleaner.

Gold
Beautiful and has a great feel, but it is a softer metal and not well suited for chain maille if each ring is not soldered. Gold-filled wire and rings are a great option for both the strength to weave maille and a durability more like solid gold (gold plated will wear through in placed in a year or tow on average depending how often you wear the piece). Gold-filled is wire made of a base metal core and then the outside 1/20th (5%) of the wire is made of 14k gold. This is MUCH thicker than gold plating and will not flake off.

Niobium
This is a metal similar to titanium in purity, but has a weight and feel more like sterling silver. It is a little pricier, but worth the cost. It is anodizable in many bright, amazing colors (and one of the metals I can anodize myself for custom colors!). Niobium is hypo-allergenic, so it is a great option for people with metal sensitivities.

Titanium
Strong, light weight, and hypo-allergenic. Titanium is a little pricier than stainless steel, but less expensive than niobium and sterling silver. It is anodizable in many colors (and another metal I can anodize myself in custom colors!).