Ford TDCis have had quite a few problems with injectors and the value/age/mileage you're looking at puts you in that market but of course they sold by the bucket load so that doesn't mean they are inherently unreliable just that some are. The Octavia 2.0PD diesels are to be avoided, just look at the Octavias with common rail engines for better reliability. Both are good cars, I've had both a petrol Octavia and a diesel Mondeo, both estates, both had plenty of room, Mondeo a much better drive. If pushed I would choose a petrol Mondeo unless I was doing 20k+ miles a year but I wouldn't choose a diesel Mondeo with 80k miles on it I'd be looking for an older but well serviced VAG 1.9PD, 5 speed manual engined car, Passat, Octavia, Superb to get the potential reliability and proven excellent economy.