Born in 1972, I grew up and still live in Namibia, Africa. Growing up we had them all, from a series 1 (Which was still doing daily work on the farm until we sold her about 4 years ago) all the way through to the Defender Puma. On the farm we still have a Series IIa in daily use. I have a Defender Puma 2.4L, but my all-time favorite, and still my daily driver, is my 1996 TDi300. It has about 400 000KM on the clock. She starts first time every time. Obviously with a puff of black smoke. So, I'm bias, emotionally connected, but both the TDi300 and the TD5 sounds like a Landy should sound. For those of you who have Landies, remember to always wave at other Landies and to those who does not have one, sorry.
You can boost the power on a 300tdi like I did with a couple of injector pump mods. After the mods mine flies! Bit more smoke when throttling but that's OK. Fit twin brake servos and light clutch mods too. Of course any pump mods you should really fit an EGT. Mine is well below the limits btw. Nuts & bolts over electronics any day for me.
Added a bigger inter cooler and a single baffle stainless exhaust to my 300tdi and had it tuned as far as a mechanical turbo can be and it goes really well. Maybe not as quick as a td5 but very respectable. I would agree it is easy to maintain and parts are generally cheap. However lets face it if someone offered you a Defender and it may be a tdi or a TD5 I’d be happy to take either.