95 is the best image quality
"The image quality, on a scale from 1 (worst) to 95 (best). The default is 75. Values above 95 should be avoided; 100 disables portions of the JPEG compression algorithm, and results in large files with hardly any gain in = image quality."
http://pillow.readthedocs.org/en/latest/handbook/image-file-formats.html#jpeg