Well, the S-class W140 (which is what the '94 is) is one awesome automobile, (a model similar probably never to again be built), but it is expensive (even still, considering it's age) and does has its warts. I look at mine (a '92) as an aging, beautiful, hooker: Too sexy and too beautiful to get rid of, but hate paying to have her as a "kept lady".
The W124 is another vehicle altogether. It is (if I am wrong, please correct me) the most popular car in MB history as far as sales in the US and for good reason. The 103 engine (inline 6) is a time-proven workhorse that is bullet-proof if you maintain it, and the cars go for upwards of 4-500,000 miles. My 18 year old 300E has more power than a lot of brand new cars, with a transmission that leaks a little but shifts smoother than most out there, and it's well over 200k and counting!

Every car is different, but if you get a well-maintained W124, you generally can consider it a good buy!

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1996 SL320 97K miles
1996 C220 130k miles
1992 500SEL 170k miles <---sold
1986 300E 216k miles <---sold