A320 Rad Nav Page
 

During a VOR DME Approch,your final course -inbound- is i.e 090 now what should you put in the RAD NAV page 090 or the radial 270 taking in consideration that controller says fly heading 060 to intercept radial 270 from xxx VOR clear for VOR DME approch RWY 09R.
I used to put the inbound course until I met a pilot who said if we put the radial would be more precise ,which one is better and appriciate any reference book.

Your friend wants to display the outbound radial on a VOR receiver when flying INBOUND? It's very true that you follow the 270 radial, but your course inbound is still 090. Dialling up anything else than 090 on any aircraft does not make sense and will give you the wrong info, and will leave you even more confused than before! :ok:

CRS
 

Keep it simple, the RAD NAV input field is labeled CRS, that is the abbreviation for COURSE.

Technically speaking, flying course 090 to the VOR is indeed flying Radial 270 inbound.
Imagine an approach on course 090 to the VOR, but the VOR station is located 2 miles in front of the runway. While inbound on 090, you are on the 270 radial flying inbound, after passing overhead the beacon, al off a sudden you are flying the 090 radial outbound. Does your friend recommend that overhead the beacon you have to quickly adjust your RAD NAV entry?

Your friend may be mixing up the situation with an intercept leg, there the system asks whether you want to intercept the "radial" inbound to or outbound from the point. (used the quotation mark because such a "radial" can be drawn based on any waypoint, not just VOR beacons).

The CRS input into the RADNAV page has nothing to do with accuracy, but with proper orientation of the head and tail of the needle, to/from indication and sense of the deviation indication.