Daniel
If it' s the settings I mentioned earlier, leave it set to iMac. The imac profile contains information about the luminance of the monitor as well as characteristics of its response. Whilst generic it does contain specific information as to the way the iMac screen responds. sRGB is a reference colourspace and knows nothing about your iMac or any other monitor.
If however you want to know what colour space to save your images in then sRGB would be a way to go . It's an international standard that enables images to be easily transported from one computer to another and keep the image data intact.
Hope this helps