from what i've read most people tend to bag the sr20 interms of reliability. Ca18's tend to be stronger but the sr20 has the extra capacity. You pay more for the sr then the ca, but more aftermarket goodies for the sr20 from what i've seen. 160rwkw is about the limit for bottom ends in the ca18det.
I'd go with the ca and spend the extra money on goodies for it. If you have to go 2litre go with the 3sgte over sr20det.
or prices check out (moderators if mentioning these places is an issue feel free to delete links)
Jaustech.com.au
justjap.com
www.sssautomotive.com.au
4a's not that good?? errr, ok then.
4age, 4agze, ca18det, sr20det, 13b, 13bt, 3sgte........ how much do you want to spend, what do you want to do with the car (straight line, track, allround).
I'm thinking ca into ke70 cos its cheap not cos its better, i find the gze's better but on my budget build the CA seems to be a better option at the mometn. I'll decide fully when time comes to buying halfcut though.