I recommend the 43mm. I use this as my "normal" lens. I made a decision a few years ago to get back to basics and generally only shoot with a normal focal length prime. My thinking was that if all the old masters could get by with only a 50mm prime, then so should I. Plus I get a little exercise by zooming with my feet.
I did actually get the 31mm to be used as my normal (being the closest to the 50mm focal length used in FF), but have found myself using the 43mm more. I guess it's personal preference. I always preferred a slightly tighter shot.
The only problem with getting one of the amigos, is that eventually you must have all three!