Personally, I like the Aegis shield because of its' adaptive resistances when used in the Aegis set.
If you're not using the full set, of course, then you might as well go with a different shield. I've mostly stuck with Covariants... but I'll admit to some curiosity. What shield works best for Sci/Sci Captains?
In PvE I tend to run with high weapon power most of the time (shields and aux medium, engines low). As such, my shields regenerate slowly at best without the use of shield-boosting powers. I don't intend to PvP much until some PvP fixes are in... like improved queues... but if I did as part of a team then I'd mix it up and go for high aux, medium shields and eng, and low weapon power.