Hello Abubakar Naveed! Here's the answer:
Wi-Fi tethering: (he best option)
Wi-Fi tethering to your iPhone or cellular iPad is the best method to use. All it involves in enabling your Personal Hotspot on either of those devices and then finding the network on your MacBook or PC. The best part is that, if you use Mac, you can use Instant Hotspot, which lets you bypass the password requirement altogether (yay, Apple ID!). Wi-Fi is the only option that'll let you tether one iOS device (iPhone/iPad) to another.
Wi-Fi will provide you with the fastest connection, and a more reliable one than Bluetooth. That being said, it will be the biggest battery suck of the three available options, especially when you're tethering more than one device.
Bluetooth tethering
You'd only want to use Bluetooth tethering when you want to conserve battery on the device with the connection (iPhone or cellular iPad). It's fairly slow, and you'll only be able to connect one device at a time. All that and, unless you have an older iPhone or iPad, Bluetooth tethering is fairly superfluous.
