Personally, my experience with the CA18 has been pretty good.
Not saying the SR was bad, but considering my goals, I feel the CA18 can achieve them for less $$ than the SR20. IMO, the SR is becoming like Honda swaps. Serious spike in price (2 years ago, S13 blacktops were sub-$2k, now you're lucky to get one for under $3k) whereas the CA18's are still on the inexpensive side due to unpopularity (there, I admitted it, haha). And whoever believes that
all CA18s are older than SR's, well, they're full of misinformation. UK-spec CA18's were produced until 1993 (one of my CA's is a '93), since that was the engine in all of the UK-spec S13's. They cost more than J-spec engines, and some feel that they're not worth it. But considering the fact that I have friends that are US military in England, it's easy for me and a bit more cost effective to get parts from England than going through a vendor that deals out of Japan. I also have a personal theory that the UK-spec CA's are better than the J-spec CA's due to the head design (UK = 4 runner/4 port open vs J= 4 runner/8 port w/ butterfly valves). I plan to put one of each to the test over this summer, although I already feel that I'm going w/ the UK engine in the end.
I dunno, I'm neutral on the subject when explaining it to others. I try to put out what I know about the CA18, and let the user decide. It's all about what you want your car to be. I want a lightweight road race/HPDE car that I can enjoy, so I feel that the CA18 is my best option.
If you're interested in UK-spec CA18's, check out:
www.sxoc.co.uk <---UK's largest s-chassis site
www.horsham-developments.co.uk <---ECU reflashes, tuning work
www.norrisdesigns.co.uk <---internal parts, did my head porting
www.driftworks.co.uk <---not CA18 specific, but has a decent classifieds
Again, I'm not trying to press my opinion on anyone, I'm just putting out the info that I've gathered over the last few years that I've been researching/planning/building my car.
I hope this helps you!