You may want to narrow your model year, the S class changed body style on 92, the 126 run from 1981-1991. For model year 90-91 the model include 300SE, 300SEL, 420SEL, 560SEL. For model year 92-93(140), the model include 300SE, 400SE (92), 400SEL (93), and 500SEL. Not to mention there are diesel model offer on both the 126 and 140.
I like both the 126 and 140, for reliably, the 126 is cheaper to maintain. There are many related posts on this forum on either models.