I've been to Gilboa, Portage, and Whitestar - as has been said by others, they all have their advantages - here's my quickie on all three:
Gilboa - as for diving, it's my favorite... great facilities (hot showers, flush toilets, platforms, tables, burgers/dogs/drinks on site), you can camp right there, and there's lots to see underwater, particularly tons of huge trout. Downside - it's gotten really expensive. Camping + diving + 8 airfills (4 for my wife and I) ran about $200 - that seems excessive for quarry diving.... As was said earlier, dive midweek or VERY early in the morning if you want any sort of vis...
http://www.divegilboa.com/
Whitestar - nice place... I'm pretty indifferent to it. Not as much to see underwater, not as many fish (but lots of crawfish), camping is available but across the street (you'll need to drive between campsite and quarry). Decent entry points, and the water has a much more pleasant "tropical blue" color rather than the "icky pond green" of other places. This is run by the parks system (although has a privately owned [I think] airfill station/mini-dive shop on site).
http://www.scpd-parks.org/whitestar.htm
Portage - Not too sure how to describe this - everything is a bit lower-key here (which could be good or bad depending on what type of person you are) - there doesn't seem to be as much to see underwater, no running water on land... There is a beach and sand-volleyball courts which are good for surface intervals or non-divers. You can camp here.
http://www.portagequarry.com/
Overall, I like Gilboa the best since it pretty much has everything I want in one place - only disadvantages are the weekend crowds and the price, but all three quarries have their own characteristics and are worth a visit at least for some variety - they're all different.