Most of the time singles are a bit more aggressive than doubles, but also less efficient. So I would suggest you go for a double.
That's a rule I've learned, but it can be different from company to company.
It also depends on how thick the wire is, what kind of wire is used (flat/round), how the wires are wrapped around the armature, how the armature is balanced, etc... Those things are factory secrets most of the time, so you don't really know what it does to a motor, unless you've got a dyno.