Here are my notes from when I was comtemplating the exact same purchase:

97 C230 eng/chassis 111.974/202.023

Negatives- first 722.6 tranny

98 C230

Advantages- first keyless, no antenna, FSS, HVAC

94-97 C280 eng/chassis 104.941/202.028

96 negatives M104 head gasket
97 negatives M104 head gasket, first 722.6 tranny

98-2000 C280 112.292/202.029

98 advantages keyless,no antenna, FSS, electronic HVAC
2000 touch shift, electronic HVAC, sorted out 722.6 tranny
Negative M112 harmonic balancer

I decided on a used 2000 C280, purchased 6/2005 w/ 35m now 65m and I think it is a very nice dependable car. I think of it as a Toyota-fied Mercedes. Light handling, light P/S, quick, modern electronic tranny and electonic HVAC.

Besides maintenance, this is what has been done to the car:

35691 purchased car

44,436 bank 2, sensor 2, driver rear o2 sensor ($86)
44,715 thermostat
45,250 camshaft position sensor, old one OK ($78)
fuel pump relay, old one OK($17)
45,550 crankshaft position sensor ($80)
59,850 change plugs, all have sticky varnish on threads, 2 plugs closet to driver side fouled
62,550 check plugs 1&2, dry but oily threads, bit of carbon deposits on #1, change wires #1&2
62,641 change rest of wires ($133)
63,254 o2 sensor bank 2, sensor 1, driver front ($79), code P0150
clear codes P0170, P0173 fuel trim bank 1&2 ==MAF
63,422 MAF insert ($150), fuel filter 35

glenmore
1991 300CE
2000 C280
1990 LS400