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.

The recording by Michelangeli with the Ravel and Rach 4; it is the Ravel Concerto that the Penguin guide is praising, not the Rachmaninov. It is worth getting for the Ravel for sure.