It depends. Dansdata actually found a couple that did run. However, decent pastes (Arctic Silver, FI) and generic pastes (Radio "I need some NOW!" Shack) work fine. Pads are harder to clean off, too.
I'm personally fond of Arctic Silver Ceramique. Thick, easy to use, non-conductive, non-capacitive.
Pads are better for OEM installs, because there is only one possible point of failure: the user. If it has tape over it and you leave it, that's the only way you can screw up the installation. Any other explanations are FUD and/or half-truths--kind of like the heatspreader being good for cooling

.