Hi Andy,
I have been to both, and both are very cool. The Yukon is a fairly deep dive. Not much growth, but lots of cool stuff to see if you like ship wrecks. If you are Wreck Certified or have experience penetrating wrecks, then the Yukon can be really fun. I will warn you though, it can be very dangereous too if you don't know what you are doing. A friend of mine who was a tech instructor died on the Yukon last summer.
The Ancient Sea Cliffs are massive walls pretty much in open water. Fun to explore with a variety of marine life.
In both cases, make sure you have a safety sausage with you. I believe Woody (if he is still owner of the Lois Ann) requires divers to have one with them. Also, viz varies greatly and can't be gauranteed at both places.
Be safe, watch your depth, and NDL!