i'd say heat. it'll loosen it up so you can maybe get it out. a humidifier might help too if you have one. if not, turn the shower on high and hot and keep the door shut. it'll open it up for a few minutes at least!
Cold... I was just at the dr for sinus infection.. The cold helps shrink your sinus membrane and will help relieve the pressure.. I asked about that because when I was outside I felt ALOT better compared to being inside. I was driving around with my window down in 20 degree weather. Which seems crazy considering my head was killing me, and my eyes were achy.. But it felt better in the cold.