sRGB for both online display and lab prints.
For Web Display
For the most consistent display across all devices, we recommend saving your images in sRGB. sRGB is the standard for digital image display, it will ensure your images are displayed correctly across all browsers on all devices. Other color spaces such as Adobe RGB, might cause your images to look washed out in certain browsers.
Our lab-fulfillment partners (WHCC and ProDPI) recommend saving your files in either sRGB or Adobe RGB. For detailed information on Color Management with WHCC, visit here.