The iPod Touch only supports 802.11b and 802.11g wireless. There'd be no benefit in an "N" router if it's only being bought for the iPod.
If you're planning to eventually use other wifi devices such as laptops, then a "N" router might come in handy in the future. However, when even a single "G" or earlier device coexists with "N" devices, the overall throughput for all devices on the network will degrade somwehat.