I set up with WHCC for when my time comes to print. I was sent there by a local portrait photog I hooked up with. The service is excellent. He had nothing but great things to say and has been a customer for years.
I sent them 5 photos they printed for free to use for testing output and calibration. They sent me also samples of their paper and a nice packet. The packaging of the photos was very good. As a new customer, I was happy with service and set up and products offered, and a pretty neat online account system which makes things easy.
I don't have a lot of experience with them yet, but word of mouth is nothing but great things. He stated the cost is very profitable for him. Is it better than others listed? I have no idea. I would definitely trust any site recommended by a trusted member though, and you can't go wrong with KmH's suggestions.
I think the main difference between a lab and say costco, wal mart, etc, is that the latter uses inkjet printing. I could be wrong on that, I know wal mart does. The "self serve" stuff you can get just will not ever compare to a lab...a lab that is of good quality.
Oh, also one thing that attracted me was guaranteed 48 hour. You get your prints back in 48 hours. To me, that was a win. I don't know about turnaround on the others listed...but I'd rather wait 48 hours for a high quality product than get my instant gratification with a crap product.