In conventional cricket sense a simple way of choosing the right handle is dependent on your height. Anyone over 6 feet should pick a long handle and anyone less than that a short handle.  Essentially long handle bats are only an inch longer than the short handle bats.

But there are other factors to consider too. Like, which ball do you play with , generally it is considered better to use long handle for light tennis cricket as it gives you better swing and power needed to send the tennis ball out of the park.

Additionally it is also important to look at the shape of the handle, an oval handle is good to help against bat turning in the hand. Whereas a round handle works for bottom hand players. 

If you are looking to buy long handle bats suited for hard tennis balls look no further than gr8 1983. Made from kashmir willow, this bat provides adequate handle length to give you a baseball like bat swing.