What are some of your favorite smartphone features?

It's fascinating to me to look back just a few years ago and see where smartphones were then compared to where they are now. Isn't it funny to think that the iPhone didn't feature video recording until the release of the iPhone 3GS in 2009? Although it might have been late to the video recording party, it was still a feature that was rolling out to smartphones at the time and still made a worthy feature. Obviously, we are far past the days where simply having video recording available was a major feature, but as each new smartphone gets released it seems that some new crazy feature is going to be the "next best thing". It's what keeps new phone releases interesting.
I mean sure, we're going to get some duds every once in a while - not every feature in a phone is going to be a big hit. But even if a feature isn't a big hit with everybody and is never featured in another smartphone again doesn't mean that somebody, somewhere didn't enjoy that feature. As many smartphones as I've had, I'm sure there are a few features that I enjoyed a lot more than I should have, and in this modern day where we have so many features to choose from, it seems like a good time to discuss which ones stand out to us as being our favorites.
I'll start with my current favorite feature on the phone that I currently use as my daily driver, the HTC One. There are plenty of great features that this phone comes with, but the one that I constantly notice the most and the one that is the most pleasing to me is the dual front-facing BoomSound speakers. Honestly (and I know I've made mention of this before) but I don't know how we managed to go so long without making this a standard feature on all smartphones. I've always had a small, single speaker on the back or bottom of my device, and in most situations where I wasn't in a quiet setting it would be very difficult for me to hear any type of audio from the phone. This isn't an issue with the speakers on the HTC One. Every time I open something that requires audio, a little smile sprawls across my face and (I swear a tear falls down my cheek). It just sounds so beautiful.
The HTC One has a lot of good features worth mentioning, but I think the front-facing speakers is the one that really stands out to me every time I use it. My other favorite features in a smartphone actually come from other devices, one of which I haven't even technically owned.
I was convinced from the start that I would hate the Moto X. Always on sensors? No thanks. But when one came to me in the form of a review unit I soon came to realize that there is some good that can come out of such a feature in a phone. Being able to talk to your phone and have it respond, all completely hands-free, was actually pretty cool. Admittedly, saying "OK, Google Now," wasn't exactly natural and I wish that there was a way to change how you address the phone; that being said, it's still one of the cooler features that I was pretty comfortable using after a few tries. It's especially handy when your hands are full. I hope that the hands-free technology that the Moto X has is the first of many phones to use it, because it really is pretty cool.
Another favorite feature of mine came with when I used the Galaxy S4, and that was Air Gesture. I'll have to be quite honest with this one, though; although I thought the feature was cool, it wasn't something that I used often or found to be any easier than just touching the device. Really, I just thought it was a fun feature to show people. I think perhaps in the future it might be more useful, but for now it does just seem like it's there just because it can be... I think a lot of people call that a "gimmick" in this industry. But at least it's a fun gimmick, right?
There are so many smartphones out there that have unique features now. It's hard for all of them to stand out to me at once, and there are plenty more I would like to talk about. Those three were the first that stood out in my mind, so I suppose it's only fair to call them my favorite in one way or another.
But now it's your turn, readers. What are some of your favorite features in smartphones? It doesn't have to be just your favorite features in your smartphone - just any features at all will do! Let us know your thoughts in the comments below!