Lots of info in this thread. Started off about back roll kite loops but still worth a read
www.seabreeze.com.au/forums/Kitesurfing/General/Back-roll-with-back-loop-advice/

Depends whether you are just learning - or have been "looping" for a while.

The later in the jump you loop - the less likelihood of your kite returning and you having a nice landing, but there will also be less power from the loop.

Less power in the loop after the apex than before...
Sending the kite into a loop whist you are still on the way up will result in a wider longer loop as the kite face is more open to the wind...

Looping the kite after the apex whilst it is directly above you will result in a small arc as the kite pivots directly above you.

A kite loop just before landing can turn a rapid decent into a softer landing. A kite loop on the way up will send you down wind fast