Preserve embedded profiles for RGB, since much material can come from varied sources. Default RGB as sRGB since this is the only RGB that can ligitimately exist without an embeded ICC profile.
For CMYK normally preserve numbers. In some cases I would preserve profile, as in repurposing a picture... but most of the times if i need an image colour managed I would rather open that CMYK and convert to RGB, wich would bring it in line with other colour managed images.
I would not convert to working space, since that changes numbers destructively.
When opening files that missmatch Enable all RGB profiles, and if you are going to a compatible CMYK (eg staying within different coated CMYK profiles based on same measurement data) dissable all profiles assigning the output intent.
This is a method been using and teaching, find it very rare to need to make exceptions to these settings. Can be some image that need special GCR.
