My personal advice would be to go for range rover classic, around 1990-1995 200tdi. Some may have been converted to tdi from v8 but as long as it's been done properly there is no harm in this. If you get a late classic (like a 94 onwards) it will be a soft-dash model and hence it is generally a nicer place to be in (similar dash as the 300tdi disco, but without the buttons around the clocks as far as I can tell) It is more likely to have the gismos such as cruise controll, heated screens, heater electric leather seats etc. These dont tend to be too bad reliability wise, but I have heard air suspension on them is troublesome once they start going wrong and best to just convert to coil springs as that cant ever really go wrong. If its mainly reliability you are looking for, get one with the least gismos, as there will be less to go wrong.
Don't go p38 as they are not the most reliable.
Hope this helps