I was in Madisonville a couple weeks ago, and had the same choice. I took a tent, camped out at Mermet, and dove the whole next day ($5 to camp per night, and some nice rustic campsites). My reason for going there was mainly I thought I had a better chance of finding buddies, and was hoping to night dive. Got to dive with an instructor/cave diver Jim Cedar, who was a great guy, and happy to dive a simple dives with me (these were my first dives of the season, so needed to shake off the cobwebs). There tends to be more people in my experience that show up looking for a buddy there.
Cerulean seems to be the best clear warm water around that area, I know for sure they're open sat and sunday, but think they're closed on weekdays. Call and check though.
I also drove down to Blue Springs/Pennyroyal in Hopkinsville, and the water was very clear. This seems to be more of a deep/cold dive place, judging from the map they gave me, but there was some stuff 60 ffw and below. All the good stuff looked to be around 90-120 ffw (and coooold).
Have fun. I'd dive with you but I'm going to the Carolina's for vacation next weekend. Let me know next time you have drill, and maybe I'll be back in KY.
