Facebook compression is the worst I've seen - they sacrifice quality because for them every kb they save per image is massive reduction in costs. SmugMug, Flickr and other photography companies compress far less. There are a number of ways to handle compression that let you determine exactly what you want to do.
If filesize didn't matter, everyone could use lossless PNG compression and we wouldn't have this issue.
Unfortunately, we have to use JPG to get the size down and that can come at a cost.
I've found that most of our "sweet spot" compression ends up with 300 KB images.
This is typically achieved by resizing the images and then setting the JPEG quality compression to around 60% (varies by compression agent).
We use Intervention which can use different libraries, but we use the GD open source library.
But even within that, the quality to size ratio changed dramatically from GD 2.0.x to GD 2.1.x
The difference is obvious - 300 KB vs 75 KB
