Something mild because an agressive cam's powerband will be higher than the stock heads can support. The E cam is a good cam for stock headed cars, maby a comp XE264 series. Honestly, I would at least port the heads while you are there. Also, the stock valve springs will not work too well with high lift cams.
Stick with the stock cam, the stock intake and heads cannot support airflow at high RPMs. If you do switch, pick a cam that makes peak power no later than 5000 to 5200 RPMs.
The B cam I wouldn't really call real agressive, but it is a higher end cam than not. I have the B sitting on 1.7's advanced 2*, makes power from 3800-6000rpm on the stock tach.
I used to work on my friend's old 1985 GT. It had a B303 cam and performer intake on it, all else was stock, and it made pretty good power. Nice combination.