I've always maintained the notion that if you plan to park hop and you decide you are starting the day at one park and finishing at another that you need to park at your first then drive to your second.
In the case of EPCOT and Hollywood Studios, you can pick or choose where you park because they are easily connected.
The thing is, you can park anywhere you want regardless of whether you have a reservation or not. This is handy news if for example you want to start your day at EPCOT and end it at Magic Kingdom. Simply park at Magic Kingdom, take the monorail to EPCOT and then back again.
It would sound pretty much like one of those "duh" moments but I was surprised to learn how many people didn't know this.
I spoke with a family from Argentina on my last visit and one of the party was worried about leaving one park and driving to the next later in the day. I told him he didn't need to. Put your car where you are more easily leaving.
He was thrilled to realize he could park at EPCOT and then head to Magic Kingdom for the day and then return to tour World Showcase.
For the most part, all of this works very well unless you have a reservation for say, Hollywood Studios and want to park at EPCOT. The only way to get to Hollywood is to walk, take the boat, or take the Skyliner. The problem is all three options are located at the back of EPCOT and you can only get there by entering EPCOT.