90's are great but expensive, discos are cheaper but watch for rot. a G reg 90 would not be a tdi ( could have had a tdi fitted so check that its done right,,,)and you could be buying a lot of trouble, if your not mechanically minded or wanting to learn i would stay well clear as you have to keep on top of them, saying that they are simple to work on and there are some real good forums with all the info you need.
i have had a 90, few discos and a 110 , 90 was my favourite, 110 most practicle for my uses, disco most comfortable,
unless you want to heavily off road they are all very much