Best recording Rachmaninov Piano Concerto 4

I would probably go with the Ashkenazy/Previn.

Also get the complete cycle played by Rachmaninov himself if you don't already have it. Obviously sonically poor (1930s vintage), but well worth the listen for interpretation. Can't beat the original source.

Another nice performance with a different perspective on the work is the Wild/Horenstein performance. An RCA recording (my copy is GL 25293) reissued by Chesky (CR 41).

Michelangeli on EMI ASD 255. This was repressed in recent years by Testament.