I have a Fostex 4-track cassette several years ago which has been very good. I bought the Fostex instead of a Tascam at the recommendation of Musician's Friend. Nothing wrong with Tascam, there just happened to be a good buy on Fostex at the time. I have a friend that uses Tascam and is very happy with the results. Our keyboard player purchased a both a Korg D-12 (and later a D-1600) and he likes those very much.
I have been doing most of my recording at the computer, so I haven't really listened to any of the new hard disk recorders. However, If I need to buy a stand-alone, I will definitely look at the Fostex - they have features and pricing that are very attractive.