All are good. The 350SDL is known to have issue, but a 300 can be swapped in.
What is your budget? Buy the nicest car you can afford, not the MOST car.

As the Non-sarcastic posts above state, all motors well cared for are capable of going the distance.

Read this forum more, this question has only been asked a hundred times or more....

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85 300D 3 pedal. Current project.
83 300TD (need rear wiper assembly dead or alive)
84 300SD Daily driver
85 300TD almost 400k miles and driven daily.
98 E300D *sold
86 300SDL *sold and made flawless 10 hour journey to new home.