Normally we create logos in either the Pantone or CMYK color spaces. We prefer using Pantone, but can switch to CMYK if requested and we will switch to CMYK whenever there are more than four colors in the logo.
Occasionally we create logos in an RGB color model, but only if the client specifically requests RGB colors and understands the limitations. Simply, RGB defines color in terms of light while CMYK defines color in terms of ink. Color you see on your computer monitor are defined in the RGB color space. They look great on-screen, but you would have to convert the colors to CMYK before printing your business cards. Logos should only be created in RGB if there is no chance that anyone will ever need a printed copy.
When a client requests specific HEX colors, we convert those to the closest available Pantone/CMYK/RGB color.