jpeg Save Quality Box ???

I have thoughtlessly clicked that "Okay" button in the little jpeg quality box thousands of times; the information, once set SHOULD remain the same.

However, I discovered that is not always the case.

According to the KB versus MB size, I ?think? it only affected three images before I caught it; the little number square where I always keep a 10 was blue and had a zero; I did not think to see what the slider said, but when I put a zero in that square, the slider automatically went to nothing.

The only thing I can think of that may have caused this is I pinned "layer mask" in E+ to the "effects" pallet and that required me to delete two different files/folders/somethings and restart Elements; if that created the situation, what else did it change ?

I was able to retrieve the PSDs of those affected jpegs and save new jpegs over them; one really good reason to always keep a PSD. 

Here is what my box looks like:



I am unsure, but I think my option at the bottom also got changed; it now is "progressive"

Baseline (standard), Baseline Optimized, and Progressive are my three choices along with "scans"

I do not understand what any of these choices do.

Which of the three is my best choice ?

Thanks for reading.