The specific characteristics of these switches can be found via internet search. Below is a generalization of the differences:

Red: Linear, no click, light force (Lightest switch, smooth key travel, no change as you press key)
Black: Linear, no click, medium force (Slightly stiffer than Red, also smooth key travel)
Brown: Tactile, no click, light force (Light switch, feel a bump as you press down, NO click sound)
Blue: Tactile, audible click, medium force (Similar to brown switch, adds audible click with bump)

Red and Black are linear switches. Keys simply move down when pressed, no bump, no extra sound made.The Black is heavier, and resists your fingers a little more than the Red. Actuation is the point when the key press is registered and transmitted to the computer. On a linear switch there is no feedback from the switch when this happens.

Linear switches like the Red and the Blacks are often marketed as "silent" switches. But still make a good amount of sound when you bottom out at the end of your keypress. Overall, the Blue switches make the most noise when in use - probably not the best for roommates who prefer quiet. You could look for the Redragon K596 keyboard, SURARA K582, SURARA K582 RED with red switches and SHRAPNEL K589, PARVATI K591 with low profile red switches. 

The Blue switch sits at the other end of the spectrum. There is a light tactile snap, and an audible high pitched click when the key is pressed and actuation occurs. So you get both a feel and hear a click that reaffirms the keypress. To generate the bump and click, slightly more force is required to press this switch. For many people, the dual feedback is the main draw of the mechanical key switch. 

The Brown switch is a middle ground switch. It has the tactile feedback that the actuation has occured via a bump like the Blue switch, but does not generate an audible click at the same time. It is also slightly lighter than the Blue switch. For many touch typists, this is the happy medium, it provides a nice light tactile feedback for the actuation that you can feel, but does not generate additional noise.You could look for Redragon DEVARAJAS K556, DEVARAJAS K556-RK and DITI K585 with Brown Switches. 

Choosing the switch style is an entirely personal preference. For me, I wanted the tactile bump, as my first computer keyboard was an IBM Model M with buckling spring switches. I also don't want a loud typing experience. So the Brown switches seem to offer the best compromise of the 4 styles. You can purchase a key switch sampler to try the different styles,