I stayed at the Inn at the Waterpark a couple months ago and it wasn't very nice at all. The bathroom was gross to say the least! I really wouldn't recommend it. If the Motel 6 has been recently remodeled it has got to be better than the Inn at the Waterpark.
If I were you I'd take a chance on the Motel 6. Especially if it's cheaper and recently remodeled! It can't be any worse than the Inn at the Waterpark!
Best of luck to you!! Enjoy your cruise!!
I'm also cruising out of Galveston on January 24, 2013 aboard the Carnival Triumph for my very first cruise!!