depends if you mean Disco 1 2.0 Mpi, 3.5V8 carb, 3.5 V8 EFi, 3.9 V8 EFi, or Disco 2 4.0 V8 EFi, 4.4 V8 EFi, (may be bigger) or Disco 3 (dont know what engines they have)
well, i would steer clear of the 2.0 Mpi, they suffer from headgasket failure and then if this goes untreated then knock the bottom ends out (same fault as the K series rovers and freelanders have)
and the V8 are all good, they use more fuel than diesels but this is to be expected, the EFi suffer from electrical problems and the Carb suffers from wear and seal fatigue from age, but all in all they are reliable as a landrover can be