not every location can do it mind you... my local sams club and costco are oblivious to digital printing.
I don't think you can go wrong w/ either, just go for what's convenient, and that works well for you. If you want the least amount of fuss, take shots of as many various things as you can, and get them all "developed" from both places, and see which one you like better. As far as walmart goes, the quality for 4x6 is excellent. btw, i'm almost sure both walmart and sam's use the same stuff, for obvious reasons. Altho, i think if you do sam's online (and are a member), it's a couple of cents cheaper compared to walmart.
I have a canon s820 so i can have instant gratification and satin papers, but even w/ the canon paper, on up close examination, the walmart printout is much more continuous in tone (ie, no dots). I still love my s820 and pretty much only use it.. i can do borders and what i want and not put up w/ the crap of finding a place locally to print. I did an 8x10 to compare to shutterfly and it beat the crap out of it (yes, i'm plugging the printer

).
Just try it is what i'm saying, at a quarter or so a pic, it won't kill ya
BTW, never ever let ritz do prints for you... I had the unfortunate experience of having to rely on a print from them. It left the image lacking.. and at $10 for an 8x10? BLAH.
Linh