I have a 4C and think it is great - the only downside is the lack of NFC and that only a subset of sites support it, but more are implementing it as time goes on.
I'll probably pick up a 5 as one to store on a keyring for mostly NFC use.
I use four devices regularly: a Windows desktop with USB, an MBP with USB-C, a 6th Gen iPad (Lightning), and an iPhone X (Lightning + NFC).
What I'd really like to see is a small device that lets me use USB, USB-C, Lightning, or NFC with the same token without a handful of dongles to deal with. I get how difficult that is, but I've yet to see anything that supports more than one physical standard. Even USB and USB-C in the same device would solve most of my problem, leaving only my iPad to deal with a dongle due to its lack of NFC.
If you want to give it a try, we'll open source the hardware soon under CC BY-SA. It'd be great to see what you come up with.