comes down to would you like and what you want to use it for.
$10,000 - $20,000 S1 or S2 C34. I like them but I think there starting to get a bit dated....still a good car though.
$20,000 - $30,000 RS260 or M35. The RS 260 is the ducks gut's as far as I am concerned....I just could not justify spending up to $30,000 on a car that old for an everyday car.....the M35 although being a bit of an orphan sold me on luxury, strength, finish and pace. If I had my time again I would probably go for the RS260.
$30,000 - $35,000 M35 Axis RS260(low k's). The Axis is a good car and more posh than the AR-X or RX/RS....but I don't know wether it's worth the extra $5,000 for a good one with everything that comes stand on a AR-X. Low k's RS260....if you find a standard low K's one and you have the cash grab it.
again it comes down to your spend and what you want. They are all easy to service yourself.