I can't speak for anywhere else, but 'round these parts Advance is staffed by know-nothings who are just happy they don't go home smelling like french fries anymore. NAPA has some knowledgeable people, but it's pricey to walk-in traffic. O'Reilly has a couple of good counter guys, but their prices are higher than the balls on a giraffe for walk-ins. I mean, they leave NAPA standing. I beat them by $125 on four ball joints for an '04 Silverado 1500 last year, and over $110 on a pair of brake rotors for an '11 Impala Friday--my walk-in to their commercial! Oh, oh, oh... Oh my achin' ***. Shouldn't I have gotten a kiss with that?!
I've been at it since '87, and currently run a small Auto Value (a.k.a. Bumper to Bumper--same chain). There are only a few of us old-timer, raised-on-paper guys left. Happily for me and my customer base, my 20-year-old female employee is rapidly becoming one of the best "parts guys" around. She's into old cars, and learning to find parts for her AMX translates directly to her job... she's not much for paper (yet) but she's hell with an internet search. When the cranky curmudgeons in their 70s and 80s trust a young gal, that's saying something.
RockAuto... don't get me started. :p