Thanks to social media, I came across these great comparison images.
(I don't own these images. I'm only posting them for comparison's sake)
I knew they were bad, but I didn't know they were THAT bad. In fact, I did an earlier post where I did a mini experiment myself comparing Walgreens, Shutterfly & Mpix, and I was actually pleasantly surprised with Walgreens (mail ordered matte prints), and I wasn't overly impressed with Mpix. However, I was only comparing a couple of photos, and I know most photographers recommend Mpix so I'm not going to argue that! Plus, looking at the Walgreens photos above, yikes!
I will, however, put another plug in for Persnickity Prints. I haven't directly compared PP's photo quality to any of the other companies, but I was just impressed overall with the print options and value. They're one of the few companies that offer 12x12s ($1.99ea). And that's not all; they also do a bunch of unique print sizes, including various square sizes for your Instagram pix. P.S. The metallic prints are pretty dang cool.
Another company that I have not yet tried myself but that I've heard is pretty stellar is White House Custom Colour. I think I may use them next. I'll let you know what I think.