Note: This answer is based on a General Admission Floor set-up
General Admission Floor Tickets
Generally, we would advise fans to purchase floor seats if they want the absolute best, closest view. However, the general admission floor seating at the Rose Garden presents challenges.
Photo Credit: adapted from wikimedia
Unless you are planning on arriving very early, you may end up in the back of the floor -- at which point you would have been better off buying a reserved seat. You may have taller fans in front of you and you may be pushed off far to one side or the other, further limiting your view.
Best Seats Not on the Floor
To still be close to the stage, try the front rows of Sections 101 or 112. If you don't mind being farther from the stage, try Sections 117-118 and 223-224. You will have a head-on view and be more comfortable.