"Good" files are hard to come by these days. The name of the game is to produce them as cheaply as possible, and in the process the quality has really gone downhill.
When it comes to types of files, there are a ton of options. Generally files that are specifically made for wood tend to be far below the quality line for using on metal.
Something I've been doing is buying the Husky brand files set from Home Depot....
http://www.homedepot.com/p/Husky-Mul...PCFS/206313272
Here's the thing.... this set of files is marked "Guaranteed Forever".... I purchased two sets, and so far have worn out, returned, and been given a total of 11 replacement sets. I just keep the packaging and the receipt, and when they wear out, take them to the return counter, walk back to the tool section, and grab two new sets.....and out the door I go.
So far they've not said a word...just trade them out and go.