I do not envy you having to make a decision like like without having the instrument in your hands first. Also remember that strings make a huge difference in the character and tone of the sound, so listening to sound samples is a guideline at best.
All I can tell you is that buying from HMS is a good way to ensure that you get a quality product no matter which one you choose. I'm not sure where you live, but Mim's Ukes and Mainland and Uke Republic are great resources too.
Personally, if I were going to buy a Pono, I would get that from HMS. Mainly because Andrew (owner of HMS) is the son of John Kitakis who owns Ko`olau/Pono. If I were buying another brand, and I lived in mainland US, I might just as easily buy from a good shop that was geographically closer, but that is just me.
I can also tell you that my Pono is built exceptionally well, and sounds and plays wonderful. The build quality is above every other import ukulele I have. I think you will be very happy with your Pono. I have tried many different sets of strings over the years, Ko`olau Gold, Hilo, D'Addario, Aquila, Aquila Red, Ko`olau Alohi, Ko`olau Mehana, and finally settled on Worth Brown, which I like very much. The instrument itself has held up very well and has even prevented me from buying a few other ukuleles because they frankly just were not as nice as my Pono is and were much more expensive. I have had it for 8 years now...
Good luck with your purchase!