<p>I spent the last days trying to make the best gears I could but they are not "smooth" nor good. I searched at thingverse with "gear" but I see no set of gears. I would like someone to point me a good set of gears (with 5, 10, 15... teeth for example) so I can use this STL file with Google Sketchup.</p>

<p>Do you guys know any good matching gears that I could print?</p>

<p>I will be using this gear in a fast spinning matching so it would be nice these gears to be well designed to support some fast moving.</p>

<p>Also, I think in my case I would like to use gears with this shape (the white gear). Any idea why is this gear design better than the usual?  <a href="https://i.stack.imgur.com/7mHxj.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/7mHxj.jpg" alt="enter image description here"></a></p>

This type of gear is known as a "herringbone" gear. A traditional straight-cut gear is strong, but can cause more vibration as each tooth engages and disengages. A helical gear (slanted tooth) reduces that vibration as the tooth engagement is more uniform. However the angle of the teeth causes a sideways force that may be undesired. A herringbone tooth design effectively cancels the sideways forces but gets the uniform tooth engagement.
A search for "herringbone" on Thingiverse comes up with many gears of this type.
Regarding the quality, if you are not happy with the results of your own design, that's OK - gears are shockingly complex, and people make careers of gear design! However, if you have a good CAD model that just isn't printing well, it's not likely a bad STL.
An STL from a different source is likely to have similar quality with the same slicer/printer setup. You might be able to improve print quality of your design by changing settings on your slicer or adjusting your printer. I'd suggest asking a question with your current setup and specific print quality issues.