well, if I could avoid any year, it'd probably be the '86 because of that odd-ball transfer case (that NP-128). But you can swap it out for a 129 or something better.
I like the '85 because it's the first year that 'Shift on the fly' came out, and anything that was All-Time 4x4.
Someone once posted about the rear end axles 'busting loose' and there either was a common year, or a common batch that had issues with that.
I can't find the post, or the info.