I like a 12" radius, seems to be about the best all round for me, round enough to play barre chords cleanly, flat enough for a low action and clean bends and most accoustic guitars have a radius in that neighborhood so I don't feel uncomfortable when I switch back and forth. I have one guitar with a 15" radius, it's alright, the fretboard is fairly wide and it's OK for what I use it for, but for me 12" seems to be right, given a choice between a steeper or flatter radius, I would probaly choose steeper, never tried a compound radius, maybe thats the best of both worlds?