However, if you're a serious athlete, you'd probably want a different device, as neither are waterproof. So for triathlon, or just wearing in the shower, pick something like the Garmin or the Basis.
I have a Band, and within the device's limitations, it's excellent. I'm able to read and send messages while leaving the phone in my pocket (handy in Austin that has a "hands-free" law when driving). Simple Cortana queries show up on the screen, while more complex answers ("Show me the closest tailor") require you to look at your phone.