Price limits the S52 and also the fact that the subframe rips out are less with the S52.
It's not really a daily driver. I have a pretty harsh setup on the 325 and don't mind having a more racy setup on the car. I don't need practicality. I'll still have the z3... not that it is practical... at all. The 325 I am giving to my little brother and plan to buy it back in a few years to convert to a pure race car. Probably SCCA ITS or if that shitty restrictor plate is in place still, then BMWCCA JP.
I believe the M Coupe is actually the fastest. I've heard times all the way up to 5.1 0-60, not too sure about them, though. The only problem I have with the M C/R is the fact that they have the archaic e30 rear suspension. My friend has an e30 318 and I definitely prefer the live Z rear axle of the e36 325 for handling on the track. Oh, and the rear subframe failure. Great, it's even worse than the e36 rear chasis failure which really wasn't that bad of a fix.