Hi and welcome, you are looking at two very different beasts
The 2.8tdi is unrefined and agricultural but as reliable as anything, in fact its most likely the most reliable engine VX put into the Frontera.
The lump it very easy to work on (and thats not often) its getting on a bit now at 15 years but still brilliant performance from what is a 40 year old design of engine, you will find the ancillaries may need replacing with age like alternator and starter but the main lump if looked after with regular oil and filter changes will be going well when the rest of the car has fell to bits.
You should get between 25 to 32 miles to the gallon and very easy to modify.
The 2.2dti is a more refined engine and a tad more power down and newer, but its the same as most modern engines and has the ECU controlling most things this can make fault finding a bit of a problem occasionally.
The 2.2dti being the B series is a little more difficult to modify for off roading due to the fuel tank in an awkward position and from standard its a bit lower in ground height, this is because its designed more road bia, so its a toss up with your needs.
A few other views I am sure will be forth coming
