Each of the quaries have their individual charms and drawbacks.
Gilboa - Good for advanced skills, particularly deep. They also have the most stuff to look at, if you like old cars and stuff. The plane is probably the best of the bunch. Gilboa also has lots of fish, probably more than I have seen at the other two combined. Down side to Gilboa, parking is horrible, and getting in and out can be very crowded at the docks, not to mention the stairs and the slippery conditions. Up at the main office there are real restrooms and showers, but not real close to the dive areas.
Portage - I dove there once, and they considered it a good visibility day with almost 20' of vis. Platforms are very poor, if there is a class there forget it, the silt on the bottom is at least an inch thick and stirs up very easily. They do have some nice features, there is a volley ball area, and I understand they have a beach (but haven't seen it). Parking is actually pretty good.
Whitestar - Shallow quarry (max 60 feet) that has been converted into a park. It actually has a nice looking beach, although its closed for the year now. The parking at Whitestar is very convienent, lots of picknic tables and getting in the water is easy with a giant stride off the wall, or wade in at what looks more like a boat ramp. They also have a close by concession stand and air fills. They have three good size platforms for classes. Definitely the more relaxed of the three places. There are some things sunk that you can go look at. I generally go looking for crawfish and other things.
All three have vis problems, on Sundays when classes are there, vis can be real bad. I think of the quaries as a place to train new divers, practice skills and hang out with dive buddies between trips to someplace nice.
At Gilboa and Whitestar you should able to find someone to dive with just about any weekend. The one time I was at Portage it was pretty empty, but that may have been just then. My favorite is Whitestar just because it is so much more relaxed, with Gilboa a close second. Portage gives me the creeps for some reason so I don't go there, but that's me, my dive buddies kid me about it.