Well, I know I might not have the popular opinion, since everybody seems to think so highly of Nicholson files, but I think they've gone down in quality, compared to the older ones I've picked up at the flea market, which seem indestructible. Ultimately however, I've had much better experience with Grobet files.
They're a bit spendy compared to Nicholsons, but they're ace. They're available in any possible size or shape you can imagine, and in many cut grades, from 00 to 08, with much finer cuts than the american files I've seen, which'll allow you to get a much more refined finish with the files than you've ever seen with the normal file cuts, which means much less hand sanding. They've even got a special line of super hard files designed for platinum, and hard to cut stainless alloys and such, that are the hardest available supposedly, at RC 72.
By contrast, my Fisher anvil has a top plate that's so hard it ruined two new nicholson files when I tried to dress the chipped heel.
Check out this site, for more selection than you'll be able to make sense of:
http://www.artcotools.com/grobet-files-rifflers-c-256.html
Also, Lowes carries chainsaw files under the brand "Oregon" which I believe are Grobet round files, although just in one cut.