Best mode for a router
Go with:


802.11g/n


That setting covers the first generation iPad through to the latest iPad that got announced yesterday as well as the first generation iPhone through to the latest iPhone 4S. Your devices should pick the faster protocol (N) if they support it. If not, they'll use the slower protocol (G).

But between G and N you've got just about all modern wireless devices covered so your network should be friendly to everything WiFi you bring in to it.