Speed: measurement of velocity. eg. A rabbit can run very quickly.
Quickness. Ability to move over a short period of time. eg. the rabbit hopped quickly to the left to dodge the wolf chasing it.
Speed (thought one.) The quicker (/faster) an object moves, the longer it takes to change direction. (your car, taking a corner at 55mph/ kmh compared to taking the same corner at 5.5 mph/kmph.)
Speed.(Thought 2) Remember the physics of MASS. a 210 kg Uke will have a different momentum to 55 kg uke. Bowling balls as opposed to tennis balls.
Other have quoted speed makes for sloppy technique. I agree, particularly with regards of mass. (me; big and clumsy)
Lightness. I like that idea, and it is worthy of a whole new thread.
A adjustable controllable speed,being light enough to move when needed.
Speed will come with correct practice.
Anyone can do sloppy technique fast.
Sloppy technique done slow means that you can get taken apart by Uke.
My ten yen worth.