As a PP stated, it is likely going to come down to personal preference.
We stayed on site at POR for 7 trips. For probably the first 5 of those trips, we used the bus exclusively. The last couple of trips, on occasion we drove, but only a day or two out of 10 days in the parks.
We too are rope drop to park closing kind of people. If you go early for Rope Drop, generally the buses aren't terribly busy. If you are a bit later, shooting to arrive at the park right around park opening time, the buses will be super busy, so getting a seat is hit or miss. Leaving the park at park closing means waiting in a long line for the bus, and being packed in like sardines.
I have found that even at Magic Kingdom, where it is necessary to take the Ferry, or (better choice usually) the Monorail over to TTC, we can almost always make it from the park to our offsite accommodations in about the same amount of time we would have spent taking the bus to get to our onsite hotel. Additionally, our own vehicle always has good AC, it is never hot and sweaty inside, and we always get seats. For those reasons, we prefer driving ourselves.