Whatever you like. the smaller the number, the deeper the cut will be and the more the blade will grab. A higher number gives you easier turning but it will be harder to hold your position in a shoving match. 1/2″ is a pretty typical number, just go with that.

HOWEVER YOU WANT

A few factors will determine the best radius to have your skates ground to.

Usually, 7/16 is the radius of choice. However, if the ice you play on is softer than normal, you may need to increase the radius to 1/2 avoid cutting into the ice as much. If you play on a harder ice than normal the opposite is true, you may need to go to a 3/8.

What is your style of play? Do you grind in the corners? Stop and start a lot? You may want to stay with a 7/16. Too much radius, like a 1/2, and you will slide too much on your stops. A sharp radius like a 3/8 and you will dig into the ice too much, and tire easily.

It is mostly personal preference, so I say try a couple of different ones to see what suits you best.

Good luck,

Steve.