The main thing is to find one that has been loved enough to be worth
committing yourself to and don't worry too much about the year.

As Scott says, the later sliding door is a huge improvement that all 85
and newer models have. The better parking brake was phased in during the
85 model year and many 85s don't have it. Ditto for the plastic coolant
pipes and cast front lower arms. At least the newer and much better
parking brake can be easily added to earlier models.

The 86+ has more powerful front brakes to go with the more powerful
engine. Better caliper design, more pad area, larger effective diameter
rotor and of greater thickness.

The upgraded wiring found in 86+ is a more robust and versatile system
though I'm not sure too many owners would notice the difference.

Lots of small changes were made after 86 as well and the vehicle just
got a little bit better year by year. I prefer 87 and later but 85 is a
sweet spot in the value curve and 86 is only slightly different than 87.

Mark