I've run lots of all the big Disco & RR options of these as elderly (10 year old+) vehicles for prolonged periods of time clocking up probably 25k+ miles during ownership and have several now, including a lot of commercial towing. I do all my own work as I'm a commercial vehicle mechanic so only ever pay parts only plus my own spare time they never go near a dealer or garage for anything other than a 4 wheel alignment.
Based on my experience I would put them in this order of preference for economy, utility and reliability but please note all of them have a lot to go wrong compared to most regular cars.
1) Disco 2 TD5 ES spec (air susp, active corner etc.)
On this you get near RR level interior and toys pretty good ride and handling, esp cornering, with most things that can go wrong relatively inexpensive in parts and DIYable. Galactic mileages on original engine and gearbox are readily achievable the biggest issue is rust at the rear of the chassis that you would need to be on the look out for when buying and keeping on top of preventing during ownership.
2) Disco 3 / RRS in 2.7TDV6 guise- commonly held to be identical vehicles bar the body shape but not really true ride, handling and noise levels are all superior in the RR Sport
Probably some of the most generally reliable more luxury vehicles LR had produced up until that point. Yes there's suspension arms and electronic parking brake but all doable and not budget busting. These can do the biggest miles without the need for any intervention beyond normal servicing, with everything working. The TDV6 will have a chance it can spin a bearing and snap the crank at some stage but I've seen plenty over 200k on the original engine my suspicion is lots of short trips in the vehicles life may increase the risk as a lot that have come my way seem to have been used on the school run etc. TDV8 in RRS more likely to have a turbo for lunch and personally I don't find the V6 that drastically lacking in performance to justify the, much worse in reality than quoted, mpg.
3) P38s
Now I do like them very much, and yes parts are cheap. The diesel is more reliable but unrefined and not as reliable as the Disco 2 TD5 and a Disco with ACE and air susp gives a much more refined ride. The V8 petrols are, as you'd expect, very pleasing but they all let go with liner and overheating issues at some stage. If you buy a truly great example at say 120k I very much doubt you will get 25k more out of it trouble free if it's the original untouched engine and many go much earlier. Fuel economy is obviously dire LPG is better but my experience is gas converted examples are more likely to slip liners. There are top hat liner rebuilt engine solutions but even fitting it yourself you'll be into the same money as a replacement engine for an LR3 or RRS. My biggest downside to the vehicle is they will almost always have a list of things that need doing, yes the air suspension is perfectly maintainable but it needs way more maintenance than on any of the models above. Ignoring the V8 engine issues If you're doing anything approaching average or above miles you are committing to taking on vehicle repair and maintenance as a substantial time filling hobby.
4) L322s
Basically many of the issues already mentioned plus additional ones the worst of which is gearbox failure. In my opinion beyond a better interior and image you actually get nothing more, and in a few areas less than in an LR3 or RRS plus worse fuel economy, performance and reliability.
In the say £5k - £10k 12+ year old full blown LR luxury 4x4 category my pick would be a good example of an RRS HSE spec (my pick because I have tools, workshop eqpt and vehicle repair experience, in case anyone wonders why I put TD5 top of the list). In the past 15 years development has moved forward very, very little indeed beyond bodging on some touchscreens, powered tailgates, exterior cameras and a small assortment of other electronic tech. In fact, the actual real world driving experience between the latest RR/RRS iterations out of the showroom in 2019 compared to 2005 are absolutely minute compared to driving the 2005 vehicles out of the showroom against the same timespan 1991 year equivalents.