I don't think you can beat a mud or musk for activity level (always doing something entertaining), or hardiness. Indoors is a big issue as well. Some species you should NOT consider for indoor living are the north american box turtles. You would come to regret trying to house them inside with all the problems that would creep up.
Muds and musks, though, are probably the one species that is perfect for new people as well as being as hardy and interesting as any other species there is. They also have the bonus of being on the less expensive end, so initial cost is less (but of course when buying a big tank and lights and all that, you end up spending a fortune anyway)