Which carrier is best with iPhone 4S in your state?

Now that you have three U.S. carriers to choose from when it comes to the new iPhone 4S, you can afford to shop around a little for the network operator that will get the best performance out of Apple’s (s AAPL) latest smartphone. Open Signal Maps has helpfully put together an interactive map showing data from thousands of speed tests combined with information known about the iPhone 4S’s chipset. The maps shows that AT&T (s T) is the winner in 31 states, but does that include your state? Check out the map below and click through for more details.

Open Signal Maps doesn’t have data on every state (sorry, people of Idaho, Montana, Wyoming, the Dakotas, Nebraska, Iowa, Maine, Vermont and New Hampshire). While AT&T took 31 states, Verizon (s VZW) would be fastest for iPhone 4S owners in six states. Sprint (s S) didn’t test fastest in any state. At least they’ve got that unlimited data plan going for them?

Open Signal Maps does include the caveat that this is not a comparison of the three carriers’ networks vis-a-vis each other. Rather, this is a test of how the iPhone 4S only operates on each different network. Here’s the explanation:

What’s the difference? Well, the iPhone 4S is a dual-mode phone that supports AT&T’s 3G network, which uses HSPA technology, and Verizon and Sprint’s 3G network, which runs on EVDO. AT&T has recently upgraded their existing HSPA network to HSPA+, which offers almost double the speed of their original 3G network, and the iPhone 4S supports this newly upgraded technology. Verizon and Sprint aren’t actually far behind: have both rolled out next-generation 4G networks, and Verizon’s LTE network in particular was blazing fast in our recent testing. But since the iPhone 4S doesn’t support those networks, they’re not included in our analysis.