To be honest Matt (this is my first post and I'm also a Matt) you will get loads of conflicting advice about which power plant is best. Its true that if you break down in the middle of nowhere an average mechanic with a limited toolkit can resurrect a 200 or 300 TDI blindfolded but for my money a later series TD5 (2003-2006) would be my call. I've had all 3 and currently run a 2006 90 TD5 hardtop and to be honest the only issue I haven't had to deal with yet is the engine (and mine has a PSI tuning box fitted which can itself cause issues).
Surprises can hide almost anywhere in a Landy (which im told is part of the attraction) but the bits you don't want to have to deal with as a new owner are the chassis, drivetrain and major suspension components). You are more likely to come across horrors in these areas than a completely unrecoverable engine (which you should be able to spot on a thorough inspection and test drive). I would also make friends with a local specialist and get them to look at any prospective purchase before you are relieved of any cash.
I bought my first 90 (also a TD5) from a "reputable" dealer in the West Midlands who trade extensively on their brand name and global client list. Yes the vehicle was serviced and legal as i drove it out of their compound but the problems i encountered six months later would already have been apparent to a junior mechanic (and now me with a few years experience under my belt). Lets just say it cost me 30% of the purchase price to make it safe ... let alone put it right for the tasks I had in mind.
On performance and reliability ... well my current 90 TD5 appears to be bombproof. It has been modified significantly in terms of suspension, drive train and interior / exterior mods (its setup for expeditions to Norway and Morocco) ... but the TD5 power plant is pretty much standard, 86,000 miles with a PSI tuning box fitted at 80,000 and no issues to date.
You will probably find (when a few more replies come through) that the 300TDI wins the day from a hardcore fan perspective .... a lot of early issue TD5 owners retrofit the 300 when they tire of their incumbent engines legendary issues. But ask an owner of a 2003+ TD5 if they would consider a retrofit "basic" TDI engine they will almost certainly laugh for half an hour.
Long winded reply but I could find a way to shorten it without missing the point. I'm not sure where you are located so cant help re a local specialist (mine is Staffordshire 4x4).
