I was working with a student recently and was reminded of all the subtleties of uke strumming. For instance, I use my index finger, sometimes supported by my thumb, to strum. When I do a downstroke, my index finger is curled upward and the nail part of my finger drags against the strings. When I do a return upstroke, my finger points downward* and the flesh of the finger strums the strings. Thus the first stroke has a harder, nail driven sound and the upstroke a softer, flesh-driven sound.
*This isn’t quite right. On the upstroke, the finger starts out pointing downward but really kind of travels upward during the course of the strum. This curling action is part of the strum.
As I observe thumb players I find the reverse is true. They strum downward with the flesh of the up-pointing thumb and upward with the nail of the down-pointing thumb.
Just this fluctuation between nail and flesh gives a strum a specific flavor.
This video demonstrates the different sounds from nail and flesh (though that’s not the purpose of the video.)
Of course another factor is where you strum. I play a lot of baritone uke and tend to go for the soundhole. However, advice is different for different ukes. I nod to this site which says…
The ‘sweet spot’ on the soprano and concert ukes are around the point where the neck hits the body. The sweet spot for tenors is a little closer to the bridge than this.
There’s more useful info at the link including discussion on different strumming techniques like chunking, and demonstrations of many strum patterns.
Wil Forbis Music 
I actually strum with my middle finger, because I’m a weirdo, I guess. :). But, if we didn’t put our own personality into it, it wouldn’t be any fun, right?
Yeah, I’m sure every variation has been tried. It it ain’t broke, don’t fix it. 😉
Not that I know much of anything, but when I first started I had big problems with tensing up. I liked keeping my hand loose, which led to the middle finger strum, and sort of stuck with it because so far haven’t hit on any reason not to. Though, now that a friend is starting to learn, it led to some confusion. Apparently he found my chill hand position perplexing. Oops.
I imagine variations in hand structure and even parts of the brain that control movement account for people various preferences. There’s no one size fits all approach that will work for everyone.
True, I learned anatomy causes all sorts of interesting issues when I was trying to square away strap length. I have a short torso and comparatively long arms. All the internet advice was more handicap than help in my case, and it was frustrating as hell trying to figure out what I was doing wrong that the supposedly great advice was making matters worse. Every article and video said the same thing, but I felt like my arms were jammed up into a really unnatural position, and it was making it harder to play. Then I realized I’m just shaped funny, so now I just do what feels right. 🙂