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Ledgem

macrumors 68020
Jan 18, 2008
2,034
924
Hawaii, USA
USB would be fastest, followed by WiFi, then Bluetooth. There is no way to connect the iPhone to iPad by USB, so you'd be stuck with the wireless options for personal hotspot there.

The disadvantage of using Wifi vs. Bluetooth is in the timeout. After approximately 15 minutes of inactivity (when not plugged in to a power source) the iPhone automatically shuts off the wifi network, requiring you to re-access the Personal Hotspot screen in order for the network to re-activate (followed by waiting for your devices to reconnect to the network - if you leave the Personal Hotspot screen before devices reconnect then the network shuts off again). If you connect with Bluetooth then there is no timeout; as long as they are within 30 feet of each other, your two devices will be connected all day, and the tethered connection will be available.

In summary, the Wifi hotspot option is good if you only need the internet briefly, and perhaps if you need fast speeds with a phone that supports LTE (which the iPhone 4S does not). Bluetooth is better if you'd prefer a sustained connection that only requires you to pair once, and then is ready to be used at any time throughout the day. I haven't noticed a difference in speeds with wifi-based connectivity or Bluetooth connectivity when tethering an iPad Mini to an iPhone 4S, but find the Bluetooth link to be much more convenient.
 
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