If you're drawn to the soprano, that's what I'd get.
If you're anything like me, you'll fret over this decision for a while, then spontaneously buy one or the other to get over the bump of indecision, then fret again after a brief period of relief and wonder incessantly whether the other size might not have been better.
Then you should stick to what you have chosen for at least half a year, instead of (like me and many here) getting the other sizes too. But eventually you'll probably be curious; for myself I found that I could not possibly have figured out what works for me if I had not done that part of the journey.
This is why I believe that it doesn't matter where you start, and why I would begin with what attracts you the most. It will either be a perfect match right off the bat, or it will get the thing you're the most curious about out of the way early on. When you're already attracted to the soprano, you will always wonder about it anyway, so to me that sounds like a good starting point. But really, either choice is good.
Remember that you can also resell good instruments. There's a loss, but a good chunk of the money can be regained. Sopranos and concerts aren't so different that you would find one size perfect and the other size completely unplayable. Not with your hands and not with this brand.
Your preferences may also change in time. Mine have, and who knows, with more experience they might change again. That makes life exciting.
(And anything you learn transfers to the other two common sizes too.)
So, you can't really get it wrong.