Another lover of the SW3 here. The transflective display is definitely the best thing about it, and the micro USB port means I can charge it at my desk if it needs a top up. I use mine to track my lunchtime walks with Google Fit, set reminders for my sieve of a brain, see my shopping list while shopping, get Google Authenticator and Steam Guard codes, and set timers for various things.
The battery seems to be giving out though, so I might need a replacement soon, but it would really have to have:
Non flat tyre, Transflective display
Standard charging port (micro USB, or I guess USB C)
Ideally, heart rate monitor and sufficiently waterproof to be used while swimming, but could live without those.