I would have to say "none of the above" to your list especially buying one blind off Autotrader. All of those cars have known and expensive problems - head gasket, wiring harness, injection, engine management, climate control - just read the posts!
Your only hope with one of these is to find one with a known service history and a knowledgeable mechanic who can inspect the car and the history and tell you if the trouble areas have been addressed. Or see if you can find a Starmark car with the extended warranty.
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe