I love Benzes, and if it's a W124, I would say go for the 124 without a doubt. it's sedate, SMOOTh, solid and looks totally classic.
I recommend the silky smooth straight six E320 as long as: A/C evaporator, head gasket and engine wiring harness have been taken care of. The rest are rather minor. I think the w124 is one of the best cars ever...
The 500E is quite a car but maintenance is horrendous especially as the awesome M119 starts aging. I had an E420 (similar engine but smaller), which developed weird stalling issues that nobody could diagnose..
I've also had a W208 CLK55, which has the same chassis as the W202 c class on your list... I personally recommend that you look at the E46 BMW instead. the w208 is a very uninspiring chassis (even in clk55 form). BUT, it was fairly reliable to be fair.
I'm personally not a fan of the W210 e-class for one reason - it's .. not very pleasant to look at... not to mention the problems that it comes with. A good friend's parents had an E320 4matic and they were trying to give the car away...
regarding the audis: i know too many people with those older audis you listed and they always talk about what to fix on weekends
My preference:
E46
W202 c class (look at C36 AMG)