What color profile should you use?
I wish I had a nickel for every time I've been asked this question. My best recommendation is that if you don't fully understand color profiles then you are safest to use sRGB.
However, there are times when you may want to use Adobe RGB 1998. When doing so, you really should understand what the differences are and when you need to use Adobe RGB 1998. Most importantly, you need to know how to properly use Adobe RGB 1998 to avoid adding color shifting to your images.
Adobe RGB 1998 vs. sRGB gamut explained
Adobe RGB 1998 represents a broader color range than sRGB. Most of the extra color range is in the highly saturated green and cyan spectrum. Adobe RGB 1998 doesn't actually have more color combinations of RGB values. It just covers a broader range of colors. It accomplishes this by adding more spacing between colors (and possibly more color banding as a result). This is explained more later in the article.
One very important thing to point out is that Adobe RGB 1998 provides ZERO added benefit to skin tones over sRGB. If you shoot mostly people portraits then you are probably better off using sRGB because it is more standardized and the workflow is simpler. With sRGB you don't need to worry about converting for the web, whether your print device will support the extra gamut, etc.
When to use Adobe 1998-
Use Adobe RGB 1998 If you need to print highly saturated green or cyan colors that are outside of the sRGB gamut AND you have a printer capable of printing it. Basically, that is the only time when Adobe RGB 1998 will provide any benefit. For anything else, you are better off by using sRGB
Here a a couple of key things to keep in mind when using Adobe RGB 1998.
1. If you use Adobe 1998 then your image should start out as Adobe 1998 and not simply be converted from sRGB. Make sure the image stays in Adobe RGB 1998 for the entire workflow. If you shoot .jpg then make sure the camera is set to Adobe 1998. If you shoot raw then the camera color profile setting doesn't matter. Raw mode does not apply the profile directly to the raw image file. For raw, make sure that when you open the image you select Adobe RGB 1998.
2. If you want to put image on the internet then you also want to save an additional copy in sRGB for the web.
In Photoshop, DON'T use the "Assign Profile" to switch from Adobe 1998 to sRGB. Doing that will shift the colors. Assigning the profile keeps the exact RGB values for each pixel but just switches the profile used to display. Adobe 1998 and sRGB use different RGB values to display the same color.
You need to use "Convert to Profile" in Photoshop when converting from Adobe 1998 to sRGB. This will convert the RGB values in order to represent the same colors (except where it is out of gamut in which case it clips the channels). You can also do a save for web in Photoshop and use the "Convert to sRGB" checkbox. This option converts the image to sRGB but it DOESN'T embed the color profile into the image. There will be no embedded profile and it will be set to "unmanaged". The internet is sRGB by default so the color profile doesn't need to be embedded into the image.
When to use sRGB-
Using sRGB is the simplest and safest option unless you need to print highly saturated greens or cyans that are outside of the sRGB gamut. The sRGB profile is not technically better than Adobe RGB 1998. However, it is the internet standard profile, Windows standard profile, most LCD monitors have a gamut close to sRGB, and all print labs can easily print it correctly. Because of these reasons, it makes using sRGB much easier and you have more repeatable and predictable results.
Regardless of what profile you use, it's best to do the entire workflow in that profile from start to finish. When you start switching from one profile to another is when you typically will start having color issues, especially if you don't really know what you are doing with profile conversions.
What I use and why-
I do almost all of my post processing exclusively in sRGB. I put a lot of images on the web and sRGB is the standard web display. Using sRGB prevents color shifting on the internet. I seldom need to print anything that has cyans or green that fall outside of the sRGB gamut. Even when I do have an image like that, I rarely care that much if the cyan or green is not quite as saturated anyway.
However, I do shoot EVERYTHING in raw. This way, if I have an image that I want to use the extra gamut in Adobe RGB 1998, then I can still use that profile. Raw images don't have the profiles directly assigned to them so it doesn't matter what profile your camera is set to. You can export raw images directly to either profile without quality loss.
Adobe 1998 RGB Myth 1 - Adobe 1998 has more colors than sRGB
This is FALSE!!!!!
When I ask people why they are using Adobe RGB 1998 they almost always tell me "because it has more colors". This is technically not true.
With either profile you have 16.7 million colors. There are 256 levels (0-255) of brightness for each red, green and blue. Therefore, each profile has 256 x 256 x 256 colors with equals 16,777,216. This is the number of different colors that can be represented.
What Adobe 1998 does is represent a wider range of colors. The extra colors it gives you are mainly higher saturation colors in the green and cyan range. In order to do this, it needs to spread out the increments between the colors, especially in the green channel. For every change by 1 value in the channel, the actual color will change more in Adobe 1998. This can lead to more color banding in Adobe 1998. This issue can be eliminated by using 16 bit color. However, jpg does not support 16 bit color so you'd need to save as .tif.
Adobe 1998 RGB Myth 2 - Skin tones are better in Adobe 1998
This is 100% FALSE!
Both the sRGB and Adobe RGB 1998 profiles are much wider than the skin tone range. The skin tones range will NEVER be out of gamut in sRGB. Furthermore, you actually have more RGB value combinations in sRGB to represent the skin tones than in Adobe 1998. This is because Adobe 1998 has bigger "steps" between colors in order to represent a larger color gamut. This technically makes sRGB a better choice for skin tones. Although the difference in the skin tone range is probably too small to ever see in print.