I can't speak to Falling Rock, because I haven't been there yet, but Twin Quarries is not bad especially for a newer diver. There are 2 quarries as the name implies and both are fairly shallow (around 20-25'). There is a small dive shop in case you need something, they have changing rooms, and pretty clean port-a-johns (at least when I was there last). There are some pretty good size blue gills and catfish that just love to be fed. The first time I was there, the viz was pretty good in both quarries. The second time the north quarry (where nobody was diving) only had 3-5' viz, but the south quarry had good viz despite all the people diving in it. Another plus, is that the water is warm due to the shallowness, so you may not need a hood or gloves. They have fresh water jelly fish, which I saw some. There is a training platform and all the underwater attractions had lines between them so they were easy to travel between.
Have fun where ever you choose!
