I had been ordering from ARS for the last year and have recently noticed a "lapse" in their service and their quality. My last ordered took an extra week to ship and the when it did, it was poorly packed and the feeders were just about thawed out.
After reading many recommendations, I switched to Big Cheese. The mice and rats are clean, plump, consistent (size wise) and well packed. Plus, they ship on Monday and I get my package the next day.
I've used Rodent Pro and Mice Direct in the past and noticed the same issues that other people are referring to.