The short answer is to use "Baseline (Optimized)" for saving JPG files.
The long answer(s) can be found by searching the Web for "baseline standard", but here's what you need to know about PSE's JPG saving options:
JPG is a "lossy" method of compressing image files -- it throws away image data before doing the compression, so set your "Quality" option to "Maximized". That is the key setting for image quality.
"Baseline (Optimized)" might reduce file size slightly (2% or so), and might be incompatible with viewers using old technology. "Optimized" might produce better colours, but that might not be perceptable.
"Progressive" means that the image is rendered as scan lines (like the old-fashioned TVs used) so that a browser will quickly show a reduced quality image of half the scan lines while it resolves the complete image.
Personally, I never use JPG -- each time a JPG is saved you lose more and more image data because of the lossy compression algorithms. I use PNG, which is lossless.
Ken
