If you can move the wheel laterally with the weight of the car on the ground, it's either the collar nut (a possibility) or the top nut on the strut.
My money is on the latter, especially if the wheel makes noise as it is manipulated on the ground.
Here's the logic behind it:
1) With the car on the ground, there's no preload on the strut insert. Hence a loose strut fastener (in this case, the collar nut and the top nut) can exhibit play.
2) With the car up in the air, the force of the spring acts against the two mounts, holding the strut in position and making it hard to move.
This one drove mefor about a month before I discovered the problem. Started intermittantly, then got to be a sincere pain in the ass.
I'm assuming here that your swaybar links are okay.
best, whit