I have found Park Sales to be expensive, antagonistic, and unfriendly in the few times I've been there. ATA tends to be into the la-dee-da sort of cyclist. CycleLoft (in Burlington) or Landrys (near BU, also in the suburbs) are the friendliest shops around, but I've also had good experiences with Ace, and they're convenient. Paramount is very friendly although I don't have experience.