Andrew Nik,
HI Fitzhugh,
I can only speak to the tapered, triangular files I use for sharpening saws. I'm not sure how the effectiveness of these files in spring steel would translate to their effectiveness in other materials.
I've gone through multiple boxes of most of the readily available brands of saw files. FWIW, I sort of evaluate files on a cost vs. longevity vs. finished surface basis, because most decent file brands will at least cut for a little while when they're new (except for the Nicholson, Mexican made files which I find to be really inconsistent in hardness -- some of them won't even cut a saw plate fresh out of the box), I focus on how long the file will cut quickly, smoothly, leaving a nice clean surface before it needs to be pitched.
For my money, I preferred Bahco which I find gives the best performance for the dollar. I think the Pferd and Grobet "American Pattern" files are next best and comparable to each other in performance, with maybe a slight edge to the Grobet. I have used the Grobet Swiss made files in the past which are excellent, but as I recall a little pricey for me.
The very best saw files I've ever used were NOS, American-made Simonds. They would let re-profile the entire tooth line for two, 26", 8 PPI crosscut saws -- about twice as many teeth as I get from anything else. The problem for me is buying these vintage USA made files on the Web without being able to see them in person is they ahve been hit or miss in terms of what shape they are in so I've gone back to the currently manufactured Bahco's.
I hope this helps.
All the best, Mike