What is the optimal pixel size?

I know the more pixels the better and raw is best. For my private purpose usually 1MB for a photo is sufficient. But for my friends and the web I want to maximise the email quality (640 x 480). Should I rather set L + normal (ca. 902 KB) or M2 and fine (ca. 893 KB) or M3 and superfine (ca. 1002 KB)? What would you say, which of these 3 examples is the best starting point for size reduction? I made several tests and could not find a convincing solution. Some of you may have more experience than I, or have more technical knowledge on the jpeg-Format. Thank you for your hints!

Unless you have very limited storage space (either on your CF card or computer drive), I'd suggest shooting everything in Large Superfine, and then resizing to smaller images for specific purposes in your computer's editing package. If you're not printing, you can probably get pretty aggressive on the jpeg compression, which is where you'll see significant file size reduction.