As a current BlackBerry Q10 user, I would only use phones with physical QWERTY keyboard. And I feel that many people do not fully understand the full potential of physical keyboard capabilities.
Here are some of my reasonings.
1. Autocorrect will not do ****, for personal names, street addresses, passwords, numbers, and number/letter combos.
In order for any touchscreen autocorrect to work, the word first has to be in the dictionary right? I have to regularly type addresses and other people's names in my phone usage. And this is where the physical keyboard accuracy comes in. Yes, I am aware that I can add words to the dictionary, but there are plenty of times when I have to type in brand new words.
2. Physical keyboard is more than just for typing, it is a shortcut key available for launching apps, making phone calls, and in-app actions.
With BB10, I can assign a contact, or an app for each keyboard key. For instance, I can press "m" from the home screen which can call my mother. Or I can press "b" to launch the browser, "q" for making the phone silent. There are 26 alphabets. That means you can have at least 26 contact, and app shortcut right from the home screen.
Ever had to scroll to the top from the bottom of a lengthy document? I can press "t" to get back to the top, instead of manually scrolling. There are these keyboard shortcut keys assigned for all of core apps from BlackBerry.
For search function on my physical keyboard BlackBerry Q10, I can just start typing what I want from the home screen instead of having to first launch a search app, and then typing which would be the case on all touch screen phones.
With the slider, the keyboard shortcuts "can" still work, but it will be less efficient since you would have to open up the keyboard first to get access.
3. Physical keyboard phones are better for your neck.
With the way autocorrecting works, if you mess up one word, you are going to mess up your entire sentence because autocorrect nowadays takes into account the entire grammer/sentence structure.
So you still have to look down at your phone screen when you type on a touchscreen, even with the autocorrect.
And looking down on the phone for a long period of time is really bad for your neck.
Your smartphone is a pain in the neck - CNN.com
With my phyiscal keyboard BlackBerry Q10, I can type blindedly without looking down on the phone because I can feel the angled surface on the keyboard with my finger tips. Now, I do not get any neck pains even from writing long emails.
I am also a lot more comfortable walking and texting since I can look where I am going, and let my thumbs do the typing.
In order for a WP physical keyboard phone to work, the OS needs to support the keyboard fully, and make use of the keyboard, instead of just "throwing on" a keyboard.