Assuming an endless supply of Superfuel, a Fox 35 would be the obvious choice. The LA would last forever, but it lacks character. In the middle of nowhere you wouldn't need a muffler, so the Fox roaring and burping through the fun flying would keep things interesting. Wear isn't too much of a concern since food would run out long before the Fox was even broke-in.
A Flite Streak with stretched moments, a Fox 35, 4oz tin uniflow tank, 57' lines, and a EZ Just Hot Rock... Can't imagine anything else coming close for leisurely fun.