Having had an Mreg 300Tdi Soft Dash Classic and a K reg factory fit 200Tdi Classic I would recommend the 200Tdi anyday.....
All soft dash's seem to rot more (bonnets, sills, rear body cross member). Some say the 200 is a better engine all round than the 300....
The soft dash has a more modern interior but has a lot more electronic gadgetery (ABS, TC).
Avoid air suspension soft dash - they were "experimental" and not reliable. Conversion kits to springs are avaialble from Paddocks etc.
My current 200Tdi has no TC and no ABS and is very easy to work on...I'm no mechanic (marine biologist!) and I find it easy enough to work on!! I do have some knowledgable mates though!
Can't comment on V8 versions other than they require regular oil changes.
Tdi - check history for cam belt changes at 60K (or less).
300Tdi - check P gasket (coolant leak on offside of block) and cam belt mod (stops shredding) has been done - you can see why I favour the 200!
Hope that helps....