The Sensation, Fascination and Inspiration are all Fantasy class ships, which means that they are identical in layout, except in how they are decorated.
All ships hold (max cap) 2,052 passengers. The Sensation was launched in 1993; the Fascination in 1994 and the Inspiration in 1996.
Our first cruise, in Fall 2000, was on the Carnival Sensation, and we had a great time. From the pictures I've seen, the Fascination has a nice lobby atrium area (blue colour). For more pics on these ships, go to www.mytravelco.com
and look at the 360 tours of the ships.
If you're torn between these ships, you should look at the itineraries they are currently sailing. That might help you out.
Whatever ship you choose, I am sure you will have a fabulous time.