The best way to farm metal INDISPUTABLY is with an anky and a karkinos. The karkinos can throw the anky to different metal nodes, regardless of the weight of the anky, meaning that you can get up to 300 stacks in one metal run!
The Ankylosaurus is, in my opinion, one of the best dinos to tame as a low level. Not only is it the best dino to gether metal, it is also a great taming mount, because it can collect berries and can kill little things like Raptors easy. This will be one of your most used dinos when you get into the higher levels and taming an Anky as soon as you can make the saddle (lvl 40) is highly recommended.
With the recent update Ankylo can hold four times the metal because it weighs less as long as it's in ankylo 's inventory. So 100 metal will weigh 25lbs instead of 100. Also tamed Anky will have more speed than usual. Happy farming ^__^ -Geo