Flashback is a newcomer, having only opened 10 months ago (although the store's owners have been buying and selling retro video games online for the past decade). For what it's worth, the newly renovated store is the best looking of the bunch, and the free arcade games are a nice touch. Their selection isn't quite as large as Fallout's, but it's not far behind. (The only exception is their Atari collection, which lags behind that of Fallout and Game Over Games). Prices are competitive with Fallout.
Flashback offers more cash for trade-ins than most, often offering cash that is close to what other stores will offer in trade. Collectors will want to check out their stock of older games (such as Street Fighter II: Alpha for the PS2) that are still in their original shrink wrap. If they don't have what you're looking for, you can put it on their wish list, and they'll call or text you if it comes through the store.