depends on your town but i would say stay away from main stream stores. check out your used bookstores they have often great prices and huge selection of things. My town has about 5 used book stores and i use only those. millions of titles in each. return books you don't care for get some credit and buy books for a dollar instead of the 20 on the back cover. plus you'll help out a local person not major franchise.
The only two that are in my general area are Borders and Barnes & Noble, but I believe Borders went bankrupt and the Barnes & Noble near me is closing. If you have a B&N in your area, though, I would recommend it. Honestly, you might be better off going to a small, local bookstore. The people who run the place are usually friendlier and you can usually find more offbeat, interesting books.
Online Amazon, Offline and Online Barnes and Noble. But a lot of time there are also small bookstores in your town that offer better service and can order you a book.
Barnes and Noble is the best ever. & If you have a Half-Price books nearby theyre pretty great and sell other things too, plus you can sell things to them.
Books a Million (BAM)