Faendal is a chump! He kept using the wrong weapons when I wanted him to use a bow. At one point he dropped out of combat with a massive 2H Battleaxe and started going all crazy with a pickaxe and a Dwarven shield! A PICKAXE!
Each follower has a different set of specialties. Faendel is archery/light armor/sneak/one-handed. So he would naturally prefer a sheild and 1H weapon for melee, given that choice. You left a pickaxe in his inventory, and that's a 1H weapon, so....
But, you are always better off equipping your followers with the weapons and armor they are preset to specialize in. Give him the best 1H weapon and small shield you can get for him, along with the best bow and leather-class armor. Then he will be the most help to you. Giving him a big 2H weapon is the worst thing you could do, as he won't be able to do squat with it.
You can always look up everything you need to know about any potential follower, on the wiki. http://www.uesp.net/wiki/Skyrim:Faendal
Check the 'primary skills' section to see what he works best with.