- It has a string groove wide enough to avoid jamming the string when you're doing string tricks; a groove wide enough to keep the YoYo from "dying"* when you throw Loops, but not so wide that the YoYo "flies"* when you throw loops.
- It has enough friction at the axle that it returns to your hand when you want it to; that is, you tug the string or by other means let the tension off the string before the YoYo spin winds down to the point that it won't return at all.
- It doesn't have too much friction at the axle so you can get at least five full seconds of spin time while it "sleeps".
- It is dynamically well balanced so that it does not wobble, hop, or cause the string to vibrate while it sleeps.
- It has a good (relatively high) rim-to-axle weight ratio, giving it good spinning momentum, and allowing it to precess slowly.
In the (good?) old days - 1920's through 1950's - the available wood YoYos generally had narrow string grooves, close to 1/16 of an inch or 0.060". "Man on the Flying Trapeze" was popular then, but it took much careful snading and waxing of the string groove to perform the trick reliably. Strings were skinnier then as well. These days, string grooves are significantly wider (nearer 3/32 of an inch or 0.093"). String tricks tend to be easier to perform reliably these days.

Fixed axle YoYos with birch axles and cotton strings return and otherwise perform reliably and well providing you've learned how to keep the string conditioned, keeping the tightness or looseness of the loop at the axle proper for the trick you're performing. Fixed axle YoYos are not the longest "Sleepers" available. The longest "Sleepers" are low-friction fixed axle (steel, brass) Yoyos or "Transaxle" (sleeve or ball-bearing) YoYos, but some of these YoYos tend to be balky on return.

Many of us love the traditional YoYos - YoYos of the traditional shape (like a doughnut without the hole), made of wood, and with a wood axle. But wood sometimes is not of uniform density. Variation in density within either side can cause the YoYo to wobble or hop while spinning; worse, if one side is heavier than the other the YoYo may precess very rapidly and wobble or hop while it's at it! Plastic (providing there are no "voids" present) and aluminum YoYos have uniform density and tend to spin smoothly.

Trick performance is hardly the whole story. Some of my true favorite YoYos are not my best performers. They are, however, things of real beauty, quality, and craftsmanship, occupying favored places in my collection. They may be too heavy, too light, old and scarred, ready to fall apart, but I love them for all that and they're mine, mine, MINE!

I hope you have at least one or two like that in your State of YO.

* When the YoYo comes around your hand in "Loop the Loop", it "dies" if it heads for the floor and "flies" if it heads for the ceiling. The string caliper, string length, width of string groove, weight ratio (rim-to-groove), and your technique are well coordinated when the YoYo heads straight out or slightly above your hand at the start of each loop.