1.8 and 2.0 are the same as each other - but not the 1.6, 1.6 and 1.4 are Zetec SE engines, whereas the 1.8 and 2.0 are Zetec E.
Mk2's have Duratec engines and are different all together.

Trim level won't effect the engine as such, though you may get an air con pump on some, not others.

Unfortunately I think a 1.6 is the best option. I'm surprised the 1.6 is more expensive tbh, I'd have thought it was much more common.