While the D lounge may have less occupants it is also smaller. I feel very claustrophobic in the D lounge. I would use the C lounge just because they seem more airy and the restrooms are inside the facility. Also the C lounges are closer to the food court area if you decide to get a bite to eat before boarding. Once you make the hike to the D terminal you really don't want to go back. Personally I would stop by C terminal North P-Club and if it seems to busy go ahead and make your way down to the D terminal P-Club.