Question Rgb fans

First of all, describe 'best' please. As in the most powerful or quiet?
Secondly, you cannot control the RGB if it's conencted to a molex cable that is connected to the PSU (I'm assuming it's connected to the power supply). So the RGB is useless, as it would just show the default colour and you won't be able to change it.
Finally, the RGB fans need to be conencted to the motherboard, not with a molex.
 
Both. Ok so I would need the 3 pin or 4 pin one
4 pin, PWM fans. If you get a 3 pin then you would have zero control over the fans. You might also need to get a fan splitter (PWM) if you want more than one case fan if your MB doesn't have enough system fan slots. You could get a 3 pin but you won't be able to control the speed (RPM) of the fans but you might be able to control the RGB if it comes with a remote control.
 
Does your motherboard have a built in RGB controller or do you already have one? If so, which one do you have?

If you just want a steady color, then you don't need RGB and can use LED instead, But which color?

In either situation we need to know how many 2cm fans you want.