The 27.6 x 11.8 x 23.6 would be best, that is about 33 gallons and is actually large enough to house 2 adult females. The other is about 42 gallons, you could honestly have 3 adult females in that. The problem with going large is that you will require several feeding stations to insure the gecko can easily find its food. So keeping an adult female in somewhere around a 15-20 gallon alone works fine, 33 gallon is OK also with just one feeding station but if you decide to do the other, you will def want to put in a feeding station at both ends of the enclosure, or one at the top and one at the bottom.
It is nearly 12", which is fine. For these guys you need to worry more about height than anything else. But there does become a point where big is just too big and they have trouble finding food, which is why I said if you go with the larger you will need 2 feeding stations.