Valet Parking, Front Gate Parking, Preferred Parking and General Parking are your options. Valet Parking will cost the most and there are two locations, one at Frankenstein Parking which is accessed from Lankershim Blvd and Jurassic Parking which is accessed from Universal Studios Blvd.
Front Gate and Preferred Parking are outdoor lots with minimal walking to the main gate. Front Gate Parking and Preferred Parking are not much different.
General Parking can range from difficulty depending on which entrance of the park you use. I prefer Jurassic Parking for general parking, which is 99% guaranteed when you enter the Lankershim Blvd entrance. If you enter from Universal Studios Blvd, you may get stuck with Curious George Parking which is the longest walk to the main gate.