Screen Calibration

There's no such thing, as dj already pointed out.

Personally, I'm very happy with my Spyder 5. It worked before with the Datacolor software and can be used directly with my new Eizo screen as it is supported by the Eizo ColorNavigator.

For most people, one of the $200-400 devices is fine, like from Datacolor or X-Rite.

If you are concerned about ease of use, watch YouTube videos where people demonstrate the software that comes with different brands, so you can see if you like the workflow of one software over another.

"Best" depends on your specific goal for color.

If your goal is basic reliable color, for things like social media or home printing, you can buy one of the devices under $200, and that will be fine. But those are usually only profiling the display, not fully calibrating it. These are also the easiest to use because they are made for the least technical users. Many are just click and go.

If your goal is more professional control, or proper control over the more expensive wide gamut displays that support actual hardware calibration to different color gamuts, then an advanced device of $200-500 will be cost effective to get the most out of that display. This level is also appropriate when you have paying clients who expect consistent and accurate color. At this price, some devices can also calibrate projectors, TVs, or printers.

If you work with print shops or other advanced professional color workflows where contracts are signed against proofs and one job could cost $1,000,000, then it might be cost-effective to have one of the $5,000-$40,000 devices that are more accurate and precise than any of the models commonly advertised in stores. Those are literally “the best” and can match a factory calibration. This is the class of devices recommended by Apple for those who genuinely need to re-calibrate one of their XDR-class displays to specific requirements, which most people will not need to do.

I'm not sure there are any products that have all of these: cost effective, have ease of use, and have the best results.

I use Spyder2Express and am happy with it. Is it cost effective? Not particularly. Does it give the best results? Probably not, but I am not a professional photographer. Is it easy to use. I think so YMMV.