I buying car for the first time.

I am contemplating between gas and diesel.

Yearly, I don't think I would drive more than 10k-12k . mostly in the city.

Which is better? (some may say 2.0 but I def like the 6 cyl even if I am driving on highway not that often)

Maths suggest that I will save only about $20 bucks a month on gas so will take 8-10 yrs to get the price difference back.

Should I consider any other costs between diesel and gas?
Is diesel better than gas engines in long run (5-7 yrs)?

any help would be appreciated.
Thanks