Hi PC Gamer, I'm wondering if thermal "grease" is better than thermal "paste" or if they're just the same thing. I've heard that grease is better? — Frank P.
Frank, my man, don't listen to these confused souls. Thermal grease and thermal paste are the same thing. So is thermal compound, thermal goop, thermal gunk, heat paste, that gooey stuff you put between your CPU and heat sink, hot ass gloop-a-doop for your CPU-pa-doop. The terms are used interchangeably, but the brands and types vary in composition and effectiveness. You'll find grease/paste with varying types of carbon, metal, and ceramic, but multiple terms describe all sorts of variations. So don't worry about 'grease' or 'paste.'
Back in 2012, our friends at Maximum PC tested 12 varieties, and only managed to produce less than 4C of temperature variance between the best and worst. So which to go with isn't a life-or-death decision. When in doubt, the popular Arctic Silver 5 is a good choice, for sure.
Some thermal stuff is different, however. Thermite, for instance, can burn through a safe. Do not put thermite on your CPU. What the heck are you doing with thermite?
How about thermal pads? Thermal pads are also different. They're a lot easier to install, but aren't as effective as a beautifully thin layer of thermal paste (or grease, etc.). Some stock CPU coolers come with pads, because they're nice and clean, and they'll work fine. If you're installing your own CPU cooler, however, I'd always recommend thermal goop (or paste, etc.).
Thermal adhesive is also different. Your pastes and greases are technically adhesives, but not like thermal adhesive (or 'epoxy'). If something is labeled thermal adhesive, don't use it on your CPU! Your CPU cooler is clamped down, so you don't need a strong adhesive. Whatever you stick together with thermal adhesive is going to stay stuck together, so only use it if you're sure you know what you're doing—probably working on a custom GPU cooling solution.
Most of the time, you just need some thermal goop (or grease, etc.). Whatever it's called, it's just a variation on the same thing: a 'thermal interface compound.'