Dang, that's a challenging question. One of the things that I enjoy most about riding is the range of different styles.
Pick one? SC Hightower. Pedals fairly well, always reliable, forgiving/comfortable/capable on pretty much anything that I ride.
Other options: Rocky Mountain Element is great but I think I'd sacrifice its lighter weight and efficiency for a bit more suspension travel in the Hightower. Scott Gambler would be greatly missed, but unless downsizing bikes came with a complete lifestyle shift, I'd never ride it enough to warrant it as the only option. Road bike (Synapse) would be my second option because I do love riding on the road, but I'd rather have the variety of riding in the woods if I had to choose. Dirt jump bike, which is essentially a pump track bike, is just never going to get used enough to be "the one" unless my town decides to put in a pump track.