I have just changed from a 4.6 1996 mk2 (p38) range rover to a 2003 disco 2 td5, my dad still has a 2.5 diesel range rover, i also used to have a classic.
The range rover is a lot softer ride but in my experience the p38 is equally as good off road, mine or my dads have ever let us down off road and we use them around the shoot, where the forestry have been using some large machines to remove trees and they have really churned the ground up.
The air suspension can be a problem and some people remove them in favour of springs, but a bit of patience and it is not too difficult to overhaul the system and usually cheaper than the spring option. The suspension on my d2 is a lot firmer, i have the ACE fitted but it doesnt float over the bumps like the range rover. The electrics on the range rover can be a problem as they age, so much to go wrong and it usually does, also the spares are quite expensive compared to the disco.
Both cars are nice to drive, both are in my opinion equally as good offroad, but the disco is easier to live with.
Fuel around town my disco does 21mpg, my dads range rover 2.5D does 18mpg around town and is chipped but still a lot slower than my standard disco.
mark