R129; special model like a SL70 or SL73 AMG; would be really special; but would be dated and possibly missing some modern conveniences.
R230; get a simple model like an SL350 without ABC suspension. AIRMATIC isn't too bad.
R230 AMG model; get a SL55 2006/2007; bulletproof M113K engine, great 5 speed transmission. Unfortunately has ABC suspension.
R230 AMG model; get a late year 2011/2012 SL63; the 63 engine had bad head bolts in the beginning of its production; this problem was fixed supposedly with updated parts in the 2011/2012 model years. 7 Speed automatic transmission. No traditional oil-filled torque converter! Instead a multi-clutch torque converter! Very special! Unfor tunately has ABC suspension.
CLK 55 AMG - rare two door model. Very reliable with the M113 engine. No fancy suspensions; no AIRMATIC, no ABC. Just simple metal spring suspension.
E55 AMG - Just in case you want to do 4 doors; very reliable M113K engine. AIRMATIC suspension. Very proven platform. A total beast, extremely surprising and unexpected for a four door bodied car.