There are a number of metals available to make engagement rings out of, some of which are not suitable, and some of which require a bit more effort. Which one you choose will largely be driven by the colour of metal that you feel suits you best and then usually, by your budget.
Here is some information regarding the most popular types of metal in use today. For engagement rings Charlton Jewellers strongly recommends the use of Platinum, Palladium or 18ct gold.
Often referred to as "the king of metals" platinum is a rare white metal that has been in common jewellery use for a relatively short time (due to jewellers torches not being able to achieve a high enough temperature for melting). It is a particularly dense, heavy metal making it very strong & giving it great durability for engagement ring use, and is tarnish resistant meaning that unlike white golds it does not require "rhodium plating".
Also it is generally almost pure when used for jewellery (at 950 parts per 1000) which means it is unlikely to irritate even the most sensitive skin. Platinum does not require any special care other than to be kept clean with a mild detergent solution or commercial jewellery cleaner, however to bring back the beautiful shine that dulls over time a visit to your jeweller will be necessary. The only downside is of course due to a combination of its extra weight and rarity, platinum is one of the most expensive metals to use.
Palladium is from the same group of metals as platinum (they are found together) having similar characteristics in terms of colour and chemical makeup. The largest use of palladium in recent times has been by autocatalysts in eliminating the harmful emissions produced by internal combustion engines. Its use in jewellery has escalated since around 2006 when an International Palladium Alliance was formed to bring palladium into main stream jewellery production as a metal in its own right. Palladium has many of the qualities of platinum - its whiteness, tarnish resistance and durability, however another benefit is that it is very light in weight which helps make it a more affordable metal. Like platinum, palladium does not require "rhodium plating", just normal care, and so is an extremely good alternative to white gold. It is also 95% pure in jewellery use.
18ct White Gold
White gold is an alloy of yellow gold and at least one other metal (typically palladium, platinum, silver...) to change the colour of the metal to white. Its history goes back a few hundred years however it's popular use in jewellery didn't really occur until the 1920-1930's when platinum became extremely expensive and later during WWII when platinum was declared a "strategic metal" (and most non-military use was prohibited). Today it is by far the most popular white metal for precious jewellery use as it carries the weight and durability of gold but the contemporary appearance of a white metal. Over the years the quality of white gold has improved - until more recently white gold suffered commonly from an inability to stay "white" and occasionally the other metals it was alloyed with caused skin reactions, however these problems have largely been overcome. White gold is nearly always coated with rhodium plating to give it a bright, white finish and this process will need to be repeated periodically to maintain the rings original look (typically every 1-2 years)