|It depends on what you want to do and see. The park is massive - it's 527 Square Miles, so seeing the entire park isn't feasible.
The park is divided into four districts by the Green and Colorado rivers: the Island in the Sky, the Maze, the Needles, and the rivers themselves.
If you're planning on visiting the park for half day or less I would suggest visiting the Island in the Sky. It is the most accessible district and has some wonderful views.
If you're a rigorous hiker, or adamant 4 wheeler, check out the Needles.
The Maze is the least accessible but the rock formations you'll see in this section are remarkable.
The following site is very helpful:
Wherever you decide to go, you're bound to have a great adventure!!