Save to PNG (Portable Network Graphics), pronounced "ping". It is a lossless file format that uses "a non-patented lossless data compression method known as DEFLATE, which is the same algorithm used in the zlib compression library." [link]
Nothing I paint ever sees jpg compression unless someone requests a jpg specifically. Unlike png, jpg is a lossy file format that compresses itself every time it is moved on your hard drive or altered in any way. This compression soon becomes evident to even non discerning viewers. However, if you save to jpg from Photoshop then you are likely selecting the highest quality compression (a 12 on the meter in PS) and after submitting to da, the file has undergone no particularly noticeable level of compression... yet. Png excels at archival purposes, as PNGs are absolutely lossless and can be moved or altered infinitely. This is crucial for maintaining a catalogue of your work. Simply saving JPGs from da to your hard drive also heightens compression of the jpg files. However, if you upload a png, you or anyone else can losslessly download the original png file. PNGs take up more space than jpgs, though I would highly recommend saving to png as opposed to jpg. An external hard drive is a great place to store your work
And a great piece here, love the dark lighting and moody atmosphere!