Thermal pads are for long term use because they are wax based and don't degrade over time like some thermal pastes do. The draw back is that once you remove the heatsink, you will have to remove whats left of the stubborn wax. Then you will either have to find a new pad or apply thermal paste. Wax is good for a permanent or very long term solution. If you are a computer nerd, you will probably take your heatsink off more than just a few times- so wax pads are not the way to go.
Thermal paste is different. It's very easy to remove and reapply, but cheaper paste can either leak out when introduced to heat, or can dry out. Never rely on cheap paste. It can also cause a mess if you use too much of it, or can cause high temps if you use too little.
I like using AS5. I apply very little to the core and spread it to the edges. Then I apply the heatsink, and then take the heatsink off. This leaves a print of the core on the heatsink. Then I take a plastic bag or something and wrap it around my finger, and then smoosh and rub the paste on the core, and smoosh and rub the paste on the heatsink. This ensures that the compound is filling in the microscopic gaps. Then I apply some more (if neccessary) and use something flat (like a razor blade) and ensure there's a nice thin layer on the core/heatspreader and on the heatsink. Remember, THIN layer, just enough so you can't see the metal, but not so much that it will squish out and make a mess everywhere when you lock down the heatsink. Once I mount the heatsink, I set my thermal paste by doing some benchmarks and stability testing for several hours (usually overnight). The constant CPU load ensures high temperatures which breaks in the thermal paste. Once I see my CPU is stable at stock, I start overclocking and tweaking.
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