With the exception of the LSE model (which had a longer wheel base and air suspension) the Classic Range Rovers and the Discovery are pretty much the same vehicle with a different body (and even a lot of that is very similar).
When the two overlapped in production the Disco always lagged behind on features and would always have the cheaper options. The Disco, for example, still used carbs on the V8s rather than EFi. This was done to keep the "premium" that the RRC attracted over the Disco on the forecourts. The Disco was launched in 1989 and ran alongside the RRC until 1994 (ish) during which time it was intentionally kept as the "poor relation" of the Range Rover.
When the MkII (P38) Range Rover came along (in 1994) and the RRC phased out (in 1996) the Disco was given a facelift with better engine options and so on to basically take over the old RRC slot now that the P38 had lots of new toys. This face lifted version is known as the 300 series Disco as it had the 300TDi engine instead of the 200TDi. The V8 option was updated at the same time using the same 3.9 V8 engine that the later Range Rover Classic had used. (The P38 had been given a better 4.0 V8 and a better 4.6 V8 so the Disco was allowed to upgrade too).
In 2000 ( I think !) the Disco was given another tweak to catch up a bit on the P38 and the Disco II was released with a longer body to meet the new forward facing seat requirements and air suspension at the back. It was also given the smaller of the two P38 V8s or a TD5. This was all done to reposition it a bit prior to the new generation Range Rover to be launched in 2002 and coincided more or less with a re-modelling of the P38.
So, with that in mind, a RRC and Disco of the same year will mean the RRC is probably a better vehicle with a better engine and more advanced features/interior BUT where the Disco really scores is post 1994 where the RRC sales had all but dried up. Hence the much higher availability of Discos that are affordable, manufactured between 1994 and 2000.
Bet you wish you hadn't asked now
