Kaitsu once said in these forums that most (upper level) blades now come unsharpened from the factory, so the skate tech can give you what you want without wasting metal changing the ROH. I checked with 2 or 3 blade companies (I don't remember which), and they agreed.
BUT, I think some very cheap lower end blades do come sharpened.
If what you are really asking is what ROH you should choose:
7/16" is probably most common ROH for figure skates, 1/2" for hockey skates.
But there are specific reasons to choose smaller ROH, and to keep your blades sharper in general, like low skater weight, narrow thinline dance blades, harder (lower temperature) ice, or rough (poorly maintained) ice. If you tend to slip sideways, smaller ROH might help - though in many cases that just means your edges weren't sharpened well, have gotten bent over, or you don't sharpen often enough.
And there are specific reasons to choose larger ROH, like high skater weight, stronger, aggressive skaters who are strong enough to push harder, softer (higher temperature) but still smooth ice, and it lets you glide faster and longer. Larger ROH blades also tend to wear out their edges less fast, so your blades may last you a little longer.
But like a lot of things in sports equipment, it is also a matter of individual taste, and there is no such thing as a consensus view. But a good coach who sees how you skate might be able to advise you better.