One of my concerns with the Apple Watch is music playback. I've had the Pebble Watch for over a year and I use it heavily for audio playback control on the iPhone.
The Pebble has four physical buttons and no touch interface and that's going to work better for me than the Apple Watch. Other than telling the time and getting notifications on my wrist, controlling audio on my iPhone is the next most used feature of my Pebble.
I wear headphones constantly while commuting, working, walking or whatever and my iPhone lives in my pocket as much as it can. The majority of the time, the Pebble is in the Music app on the Pebble. There is one button on the left and three on the right. The left button lets me go back to the previous menu, which I do on occasion. But the three right buttons are a killer feature for me.
When connected via Bluetooth to my iPhone I can pause/play, track forward, track back, volume up and volume down without having to look at my Pebble or iPhone. The middle button acts as pause/play and changes function for the top and button buttons. The top button can either be track back or volume up. If it's track back and you press the button once, it will go to the beginning of the track. If you hold down the middle button, you feel a vibration and the function of the top button has no changed to volume up. Similarly for the bottom button. It can either be track forward or volume down.
I use these buttons constantly through my day.
That's for when I'm listening to music. Podcasts are a little different. For the track back and forward buttons, instead of going to the beginning of the podcast, they skip 30 secs back or 30 secs forward. If I missed something somebody said, I can tap one button and listen to that 30 seconds again. I've never looked at my wrist. I just felt for the button and tapped it. If somebody comes up to talk to me, or I'm walking into a bank (for example), and I want to pause my podcast or music. I feel for the middle button and pause the audio without having to look down.
This is where my concern for the Apple Watch comes in. When I'm wearing my Pebble, one of it's killer features for me is the audio control. I hardly look at the Pebble to find the buttons on know which buttons to click. I can, and have, controlled music playback in the dark. I've even caught myself at a house party controlling music playing from my iPhone through a speaker system through from my Pebble. The conversation didn't have to stop. I heard a song I didn't like and quickly tapped one button to go to the next track.
With the Apple Watch's touch screen and digital crown, I don't know if that's going to work out so great for me. I would have to look down every time to scan back 30 secs in my podcast to find the touch target and skip tracks. Or finding the right area to pause the audio. Right now I just need to tap one button without thinking.
One thing that could be interesting is if podcast app developers take advantage of the digital crown. We know that it can be used to zoom in and out and control the volume. But if you could have change the behaviour to jump back 15/30 secs if the digital crown is flicked up or skip forward if flicked down.
There is another button on the Apple Watch, which only brings up your favourite contacts - so I don't think much can be done with that.
TL;DR All this to say, I use my Pebble heavily to control audio from my iPhone without needing to constantly look at my wrist . With the Apple Watch relying heavily on the touch interface, I don't think it's the best choice for me today.