There are over 14 ways to convert color to black and white.
1    Raw Conversion
2    Convert to Grayscale
3    Convert to Lab then convert to Grayscale keeping the L channel
4    Desaturate
5    Channel Mixer
6    Black & White Adjustment Layer
7    Dual Adjustment Layers - Dual Hue / Saturation
8    Dual Adjustment Layers - Hue / Saturation with Selective Color
9    Dual Adjustment Layers - Hue / Saturation with Channel Mixer
10    Triple Adjustment Layers - 3 Channel Mixers
11    Gradient Map
12    Calculations
13    Apply Image
14    Channels as Layers
Some of these methods aren't optimal. Some are equal. Some are superior.
Which should you use?
It depends on the image.
Sometimes a simple solution will do just as well as a complex one.
Sometimes you need the power of a more complex solution.
Here are my four favorites, ascending from simple to complex.