A jpg at 100% woujld be "uncompressed" so quality will be "As good as it gets" for JPG (And the file size will be huge.....
the "big difference" between JPG and PNG is that JPG is a "lossy compression" format and PNG is a "lossless" compression format. So JPGs will be smaller files on disk than PNGs (all else being equal) at the expense of LOSING IMAGE QUALITY :) You choose the tradeoff between file size and image quality you can live with .... :)
depending on the SUBJECT matter, it's sometimes impossible to see the differrence between a 100% and a 95% quality JPG in practice, but the 95% quality file will be MUCH smaller than the 100% one.