STRING LENGTH
The “correct” string length is not based on the size of the person throwing it, it is based on the size and weight of the top (and where the weight is) and the thickness of the string being used. The number of wraps the string makes around the top has nothing to do with anything so forget about it. There is an invisible magic line where the string should stop winding for the perfect throw. This is relative to the center of gravity, meaning if the center of gravity is lowered, the magic line is lowered. Once you understand this, and how to compensate for a string that is a bit too long or too short, and how to make your own string of any thickness, then you could you size the string to suit your preferences (I prefer not to use strings longer than I am). Or, if you are Takeshi, you can use ridiculously long string just 'cause :) Just remember; long strings present challenges when regenerating, but some folks still prefer it.
IMO, most tops fit in one of the two minimum sizes listed below.
60" regular string:
Duncan Imperial
Spintastics Sidewinder / Gladiator / Blizzard
Yo Yo Jam Bulldog / Top Dog
Yo Yo Factory Acrobat
Strummol8 STB 2.0
64" regular string:
Duncan Bearing King / Rip Cord
68" thicker string:
Spintastics Trompo Ggrande / Trompo Bearing
Strummol8 Giulia
Strummol8 Titi / Sophia
Some things to remember:
Long, skinny string will force the top to be thrown slowly.
Fat, short string will allow the top to be thrown hard and fast.
If your string is too short, the top will over-rotate and point away from you when you throw it. You can get longer string or point the tip outwards when you throw to compensate.
If your string is too long, the top will under-rotate and point toward you. Same for if the top hits the ground before it is done unwinding, it will be pointed towards you. You can shorten the string (don't cut until you know), or point the tip inwards when you throw to compensate. To do this either put the tip next to the web of your thumb or rotate your palm towards the ground when you throw.
String care
The best string is unbleached cotton with a tight twist and little to no fuzziness. When it gets dirty, sticky, or starts to stink, don’t throw it away, wash it with your undies! Seriously! Just keep it away from fabric softener (makes it limp) and don't put in in the dryer, let it line dry.