I'll take a shot an answering some of those questions, though they are subjective and I'm sure others on the Board will have differing views.
1. 993 v. 996.
You can probably find an entire discussion board on this subject. In the broadest of terms, I'd say that the 996 is a more "refined" model, which is easier to drive hard well (particularly with PSM activated) which has some improved creature comforts (e.g., better AC and more room in the rear two seats). The 993 is an awesome driving machine, closer to what many think of as a traditional porsche ride with a great exhaust note (though the 996 can be restored to a more daring ride by deactivating PSM).
2. c2 v. c4.
The C4 drives very much like a c2, except that up to 40% of the power may be shifted to the front wheels by the cars computer when it senses slippage. This creates incredible cornering ability under normal driving conditions and gives great confidence when driving in the rain. Also, a c4 can be driven in the winter /snow (not relevant in CA) with snow tires and 17" rims/tires.
3. model years
In the 996, there were some reported problems with early MY 99 cars (notably an engine problem). My '99 C4 (august '99 build) has never had any problems.
4. Price:
Its a GREAT time to be a buyer for a used porsche - with the economy and the arrival of the '02 MY cars. You should be able to find a low milage '99 or '00 C2 in the 50s and C4 in the low 60s (or lower). The C4 coupe remains in somewhat more demand, since MY '02 C4 coupe will only be available in a more expensive turbo body type model. I've heard there are dealers selling new '01 c2s at or close to invoice to make way for '02s.
I cannot address the drivability difference between the 993 and the 996, never having owned a 993, but as someone who had an early 996 (Sept. '98 build, delivered in Oct. '98) that I just traded in after 55k mi. for an '02 cab, I can attest to the quality of even an early '99 996. After 3 years of daily driving, in all weather and in all seasons, the car never gave me a single major problem and never broke down. The only "problems" were minor ones that a lot of people have had, ie., the check engine light coming on (solved by a new seal on the gas cap), the air bag light coming on (solved by replacing contacts on seat belts) and a recall to fix the seal on the engine compartment lid. I also thought the workmanship was excellent. The car did not develop any rattles even though it was driven in New York City.
I would definitely recommend a well-maintained '99.
Interesting that you should ask this question. I just had an article on just this subject published in this month's der Vorganger, the Potomac PCA chapter magazine.
When I got my price for my Boxster, I was ready to get a 993 C4S or C2S. Looked at a lot and ended up driving one at the local dealer. Took a black 98 C4S out for a drive and as I said in my article, it is the pinnacle of the air cooled cars. Quick, responsive with all of the traditional aircooled indosynchracies. However, once I drove, quite by accident, a 996 I was hooked. Smooth, just as fast without a lot of the quirks that a lot of folks like.
As chief steward for Potomac I have gotten rides in many track cars. What put me over the top was having a driver in a bone stock 996 keep up with an number of prepared 993's, that said a lot. Clearly drivers make the difference, but watching our black and red groups run and seeing how easily the 996's show the way, I had to have one. Also, it was 1,000's cheaper than the C4S
Hope that helps
