I loved my 240sx. I beat the living hell out of it( with proper preventative maintenance) and it kept taking beating after beating. I can't tell you how many times i reved to redline and dropped the clutch. That stock 240 just kept going and going, I actually still have the ka24e and tranny out of it(the body is smashed up).
The crx is a great car. It is really lite, and their are many engine swaps to choose from.
The 240sx is a little roomier, you have the advantage of 2+2, and it also has many swaps to choose from. The RB26DETT, RB25DET, SR20DET, CA18DET
all thes are turbo engines and have enormous potential for massive hp, and they are easily swappable into the 240sx. There are some facts on this site explaining some of the swaps very well and also the specs of these engines.
http://nissantech.com/articles/viewer.php?id=6
That link is for the SR20DET(the most popular 240 swap)
http://nissantech.com/articles/viewer.php?id=7
that link is for a tech article on the difference on chassis models
besides all that, the 240sx is a good reliable car and is really fun to drive and drive hard
The selling point for me would be this--CRX=front wheel drive=understeer=no fun
240sx=rwd=oversteer=hella fun!
I hope I helped with your decision, good luck on the car purchase and I hope you have fun with your new 240 (I know you will get one after you test drive

)