I have just been in a similar position to this, on an identical budget and ended up going for a 90 TD5 because:
1) I will be using it for a daily drive as well as for playing and the 90 offered the best of both worlds in my eyes.
2) 110's seemed like rocking horse dung to come by, especially in decent condition
3) I tried driving both the TD5 and the 300tdi and found the TD5 punchier, and quieter too.
4) I won't have a lot of time to work on the vehicle anyway due to work commitments so wasn't too fussed about the computers et c - the chances are it would have to go in to a dealer to be fixed regardless of the engine type.
5) Despite some comments on here there are lots of TD5 on the road and as an engine it seemed to get a good review in a recent magazine article (cant remember the reference off the top of my head).
6) While a land rover engine will go on for ages, there is no escaping the fact that the newest 300s are approaching ten years old now.
I'm sure I've opened myself up for a flaming here
but there we go. I'll let you know how I get on once I pick up my vehicle next Sunday. Cant wait!