Answer,
Reliability
TD42
ZD30CRD
RD28
ZD30DI
Fuel Economy
ZD30DI
RD28
ZD30CRD
TD42
(the last two with quite some variation)
Power (standard)
ZD30CRD
ZD30DI
TD42
RD28 (by quite a bit)
Tunability
TD42
ZD30CRD
RD28 and ZD30Di (equal)
Depreceation (highest to lowest)
RD28
ZD30DI
ZD30CRD
TD42
This varies but year and model of ZD30DI, ZD30CRD, TD42 as some had extra attachments, some had less, some had program changes, different injectors, intercoolers, etc. This is just a generalisation of standard form. This is only in respect to diesel GU Patrols. RD28s also have different diffs and gearboxes. They also have a timing belt which IMO is the biggest no no for an engine, I hate the concept of a belt for engine timing.