Put me down in the ice camp. I have a long history of L4-5 herniation/extrusion due to sports injuries. Heat helps a little but ice packs really help. A fantastic, very progressive PT here in Cali recommended ice and it's worked out great. He would run me through a very strenuous core workout, then ice me for 10-15 minutes and recommended ice a few times per day during flare-ups. It worked better than heating pads, hot tubs, etc.
"He's like a man with a fork in a world of soup". Noel Gallagher of Oasis, referring to brother Liam