Are you just asking for the best format for uploading to a web site for viewing? or is the question meant to cover the storage on you PC for modifications?

These are two totally different questions.

For Web Content JPEG, or PNG are fine

For saving work on your own PC you should consider either PSD if using Adobe or TIFF so that you get no loss of detail in the photos and then convert for WEB once finished post processing. As part of the conversion I normally drop the dpi to 100 and size dependant on what your users require and sharpen at this point. Most of my files are stored unsharpened until ready for either conversion to web or printing.

Roger