The downside of websites like that is that it travels over the internet, so you're throttled by every bottleneck along the way, which can be very painful if you're out and about and your hotspot is suffering 3G speeds. Meanwhile, Airdrop spawns an ad-hoc network giving you gigabit transfers in the middle of nowhere. Personally, if Airdrop isn't an option, I use TotalCommander to transfer over my hotspot network (no internet connection needed)
Not so for WebRTC. We use Snapdrop all the time to transfer between devices, and it just gets the two nodes talking, but the data xfer is peer to peer on our network. Works great.
