The top four of the most-researched individual used-vehicle models on NADAguides.com last month remained unchanged from both December 2011 and November, as the Ford F-150 continues to rank in the top spot, followed respectively by the Chevrolet Silverado 1500, Nissan Altima and Honda Accord sedan.

However, moving up two spots from November to December was the Dodge Ram 1500, which came in at No. 5, according to the data provided in NADA Used Car Guide’s latest Guidelines report.

Next up were the Toyota Camry (No. 6) and Chevrolet Impala (No.7), each of which fell a spot from the prior month.

The Ford Mustang was static at No. 8, followed by the Chevrolet Silverado (up two spots at No. 9) and the BMW 3-Series, which remained in 10th.

Rounding out the top 15 were the Toyota Corolla, Chevrolet Tahoe, Ford Escape, GMC Sierra 1500 and Toyota Tacoma, respectively.

The Sierra 1500 showed the most growth of any model on the list, having climbed three spots month-over-month.

Breaking down the data by make, it appears luxury brands led the way again.

Used-car activity among consumers increased 15 percent for the Porsche brand year-over-year-year in December, with BMW and Audi both up 12 percent.