I was looking up prices for rentals at PHL in late October. The cheapest vehicle I could find for 3 days was the Pacifica class from Thrifty at $118 all-in. The compact is $128 all-in at the same location. The only other place that had good prices was Hertz. Using the AAA code, I could get a compact for $102, midsize for $117 and a full-size for $132.

Why is there a deal on this Pacifica class?

I don't have any idea on the "why cheapest" but my comment is take the Pacifica. I drive a 2005 and it is a great car. Plenty of room and power.
Enjoy,
Bob

Just got back from this trip. I ended up getting a Lincoln Town Car. Was a great deal considering I tried a dummy booking a week ago and found that they were asking more for their cheapest car than I paid for this reservation.

My only complaint was that they were really pushy about selling the prepaid gas option and the optional insurance coverage. At all of the rental outfits I've been to lately, they shut up after you tell them you don't want any of the optional insurance. This guy didn't and said he was going to show up the liability, and then a coworker started trying to quiz us about our insurance coverage. My mom was starting to buy into their BS, so I finally told them firmly that we didn't want to buy extra insurance. It remineded me of my dealings with Enterprise.