I originally owned the 400/5.6 ED-IF AIS which was excellent for me, but I eventually sold it when I got the ED AI (non-IF) version, which was a bit larger and heavier. Both though can't be beat for a compact 400mm that are excellent lenses.
Though I love my 400/5.6 my hope is that eventually Nikon comes out with a 400/5.6E PF that is much lighter and at least as compact with excellent IQ (and certainly a price to match).
The one good thing about the f/5.6 ED-IF AIS version is there seems to be an adequate supply of them around, though it seems at inflated prices as of late . . .