I use Fomapan 100 quite a lot in both 120 and sheet film formats. I originally decided to try it because it was cheap, but I've quickly grown to love it as one of my favorite all purpose films. I like both the 100 speed and 200 speed versions of the film but don't have a lot of experience with the 400.
I completely agree with the previous post which said it has a nice tight grain structure and doesn't get overly puncy like t-max film does. I shoot a lot of portraits and figure work and I find the film is very flattering to skins tones.
My developer of choice for Foma has always been Rodinal. Then again, I tend to like Rodinal for just about everything