My last four cars in order of ownership were a 2000 NSX, 2003 Z06, 2004 E46M3 and my current car 2006 997S. In order of preference I would rate as follows: Porsche, NSX, M3 and Z06. Cons of Z06 were build quality, interior appointments of a Cavalier (very cheap Chevy product), exterior dimensions did not fit interior dimensions (oversized - XXL), nagging maintenance issues that required multiple trips to dealership for correction, transmission had a long throw and difficult to shift smoothly (should come with a standard neck brace for your passenger), not a chick magnet but a magnet for middle age guys and for that matter guys of any age, far too common a site on USA roads and just overall no attention to detail. The pros were braking, acceleration and handling.
The Z06 is a brute and reminds me of a playground bully - poorly dressed with blemishes and foul language and no much regard for others. I drove the car for 2500 miles and traded it for the M3. I did go back and drive a literally new 2004 before I purchased the 997S just to be sure that I really wanted to spend the $40k difference.
I purchased the 997S!!!!!
If your only concern is bang for buck and brute overall performance than I recommend the Z06. Here in the USA you are considered a "man of the people" with the Corvette. Similiar to the comraderie of the HD products. I was constantly waving and flashing my lights at total strangers (other Corvette drivers).