I say check out a 126 as you can see I have two. The 85 SD has been much more reliable and slightly more fun to drive due to length. Handles rather sporty for a tank
. It also has ABS and air bag like the 124.
The 87 I had to do the head on due to so much exhaust gas in the coolant that it was not cooling. Got the improved head and did it myself cost of $2000. Total invested in the car $5000 not to bad for a cross between a limo and a sports car. With the new head and a turbo rebuild it will see all 140 MPH
As for as interior I have seen all three and I prefer the 126. The 123 looks old in styling and the 124 just a little cheaper. Also, the seats in mine are very good for the age though the 85 could use repadded due to the weight of the previous owner.
Sorry such a long post had a lot to share hope it helps.