Always try to use <button> when element is clickable, but it is not a link. Avoid <a>, <span>, <div> and other elements.
Note that display: flex works differently on buttons in different browsers, but we have an easy fix for that.
Why?
You will get multiple benefits - user can "tab" to it, and to activate it by pressing enter (that will trigger click event). There is no need to preventDefault like when you are using <a>. User can't open it in the new tab/window, using right or middle click. Screen readers recognize it out of the box.
Long story short - it is way more accessible. And when you think about it, it is actually really logical thing to do. Buttons are made to be clickable :)
Gotchas
Buttons in forms
If you need your clickable button to be in a form, remember to put type='button' to it, as default button type is submit, and it will submit your form on click. Again, you could use preventDefault, but I think this is a way cleaner approach.
Button flex maddnes
For some reason display: flex on buttons is behaving really different across browsers. It is crazy! If you don't believe me, just check the examples below.
The easiest fix is to add another div in (to wrap button content), and apply display: flex to it. From there on, you should be fine. I made a CodePen with an example. On the left side, you can see a button with flex applied directly to it, and on the right, a button with inner div and flex applied to it.
I overcame my laziness and made a bunch of cross browser screenshots. Original CodePen is included at the end.
At the moment, it seems only Chrome gets it right.
Chrome
Firefox
Safari 8
Safari 9
IE10
IE11
