We purchased the thinnest magnets and regretted it. They felt very thin and flimsy. However, the colors printed beautifully and the image wasn't pixelated at all. The turnaround and shipping were faster than expected. We also received a few more magnets than we ordered, which was a pleasant surprise.
Overall, the magnets still worked perfectly as our Save the Dates, but if I could do it over, I'd pick the thicker magnet option.