I just recently purchased an 89 so have a little insight on just that one. Others will say to purchase any that you see, and I agree. 1989 was I believe the first year for the freehub. It’s a 7 speed hyperglide with first gen 105 index shifters. Gears and shifting aren’t that important, but I believe the main advantage was that the axle on the freehub is stronger than a freewheel axle, thus better if one loads it up. I can’t claim anything either way, this is just what I have read. Axle spacing is 135mm. 89 was made in Japan.
One other thing is the 89 has the first gen 105 brake levers with return springs in the levers so that the canti springs can be Set lighter. I can say that I love the feel of these brakes. All will tell you to not pass on ANY 1000, as all are great, and changes can be made to them. From pictures, I think the earlier ones are prettier. Research may show you different brakes and braze-ons and such over the years.