Most motors are radial, and multi strand is usually used for flexibility through the slots, and although multi strand 'can'
be wound nice and flat and all in a row, it would take a lot
of effort with ten strand, and so not likely to happen.
Axial's have the same problem sometimes, but when the cores are removable, like this one, then single strand becomes
an option. I had trouble on the last motor with pinched fine wires, and shorts, like larsb said, and single strand fixed it.
On the other hand, when you get up into the 14 awg and above single strand, it gets a bit hard to work with too. I could
see using two strands instead of one, maybe. Might be easy to keep them lined up too.
I think your right about smaller wires having better fill though, as long as you can arrange them right. I'm sure I read it
somewhere,.. also better for eddy currents in high speed motors, I think.
I know I'm not getting the best fill factor with 14 awg, but the stuff is bullet proof, and thats worth a lot to me.
Lots about windings on Wiki; https://en.wikipedia.org/wiki/Coil_winding_technology
Stripping is always the problem with multi strand for sure, and the orange 200C enamel is even worse, it's supposed to be
a double coat, and much tougher. If you want to shorten, or change any connections, then you get to do it all over again.
With single strand, I can use the Dremel tool with a small sanding drum, and it goes pretty fast.
Depends on how accessible the connection is, if it's in the motor, then multi strand can be a real bear.
But then theres also the problem of soldering two 14 awg wire ends,.. it's not so easy to do very nice. I've been using a
piece of brass tubing, and crimping them inside first.