Which Engine with which gearbox?

Hi all,

Can anyone give me a brief insight as to which gearbox and engine combination is best? I am assuming that this will depend on whether it is for smooth distance driving or for off-roading. Is there a happy compromise?

Also I have seen some owners have replaced the LR engine with an Isuzu engine. Is this a worthwhile improvement?

Hope I placed this post in the correct location.

Thanks in advance for any help you can give!

in what

In a Defender.