None, they are money pits.
If you get an old banger and pay little for it then it will probably be worth the same in years to come but you will have to look after it.
Defenders seem to fetch big money, as do the series but whether they continue to appreciate or not is really down to demand for them.
I may be biased but best cheap buy, relatively simple fixup (if the chassis is good) and a great 4x4 is the D2 but it helps if you have a mind for mechanics and know all the bits that need checking and sorting. You can spend as much or as little as you like and will need a Nanocom as well.