Yes the Luna would be more equal to a AF120 not a SP120. For a radiator you want the SP120 or any fan with high static pressure as that is designed to push through the tiny fins while AF is designed to move air through a case.
The Thermaltake Luna 12 series is either a Quiet or high Air Flow series, they are not specifically designed for radiators which prefer a higher static pressure. Compared to the Corsair SP120, the SP120 is better. The equivalent from Thermaltake would be the Riing series that has high SP rated fans.
Yes the Luna would be more equal to a AF120 not a SP120. For a radiator you want the SP120 or any fan with high static pressure as that is designed to push through the tiny fins while AF is designed to move air through a case.