It’s not just preference.
It sometimes depends on what kind of tricks you are focusing on.
Sometimes your armlength has to be considered.
Sometimes what direction you mainly intend to be using.
Also it depends on how fast you want to play and how hard you throw.
…1 and 2 can both apply to one particular situation.
Armlength and direction <> If you are practicing side style tricks; armlength is not very important.
But if you are throwing front style tricks; then often string length should be shorter than for side style.
Why? Glad you asked. If you use a long string.(coming up to your chest) and you don’t have pretty long arms; if you are doing the forward mount for boingy boingy or barrel rolls, etc., you have a pretty good chance to find out your face may be in the way.(ouch).
I know you can play front style tricks with your arms extended away from your body. But it is not comfortable and doesnt look natural. For front style tricks it is probably a better option to go with the belly button length.
Side style string length is wiiiide open because there is much less chance of smacking yourself in the face or chest.
…Now something else to consider; Speed! As an example; lets just say, ‘you have a shorter string and you throw hard’. If you throw down hard; your tricks are going to happen a whole lot faster.
Whether you are playing front or side tricks; if you run a shorter string and throw hard; the Yoyo will be moving along quite swiftly.
If you are practicing smooth flowing medium tempo side style tricks; a string about 8 inches above the belly button is the right choice.
Try this; do a trick like Skin the Gerbil. Try doing the trick with a belt high string and try it with a chest high string. With either string; start the trick with a powerful throw.With the shorter string you will feel you are moving a lot faster; because you are. Even without a speed adjustment; a longer string increases the length of time between string hits simply because the Yoyo has to travel farther between contact points.
Realize the Yoyo is circling a tether point. So the Yoyo with a shorter string will move with, ‘a quickness’.
… So if you are into speed; use a shorter string.
If you are more of a Guy Wright kinda player; a longer string is the correct decision. Your tricks will just look and feel smoother.
So it can be considered preference. But that preference as often as not; factors in what you want to achieve.
As people move up the trick ladder and no longer ask questions about string length; they just learn to adjust their speed, regardless of how short or long their string.
Something like that…