Always use an Icon + Text.
The icon signifies that the item is friendly and interactive.
The text signifies that it is a menu and not decorative.
If there is not an icon then it is a link on a website, any where else there must be an icon in UX.
Microsoft on many occasions states that they've done user case studies. With who? Their managers?! The less technically savvy the user (who still has a relevant need for what is being tested) the better an actual user case study. The same is true for the most experienced power users. You want to maximize your range of comprehension of not just who is using your product/service though also how.
Look at every single menu on mobile and unless you're playing a game overloaded with stuff to waste time, you're going to overwhelmingly (if not literally in absolute) always see blank space next to the icon-only menu.
...and if for some reason you don't then the layout should come in to question.
(Real / classic) Opera's installer is a (and the *only) perfect example of an application installer. Once open a single click installs the program for people who never read anything on the screen though there are options and advanced options with minimal number of steps to achieve these goals.
Newer less or completely inexperienced users are forgiven for not having the experience to comprehend how what they're working on will expand. In such cases: do not over-commit until you have proven that what you're working on won't get thrown out the door in a year or two. Stay nimble until you discover what will stick. Once you know what sticks gracefully adapt your UX over time so you do not alienate your early adopters!
From an experienced UX designer's perspective we have a very good comprehension of UX hierarchy. The more parts of an application are used the fewer steps to access something should be.
UX masters are not only power users though empathetic power users. Full toolbar customization (toolbar positioning to other toolbars on a given side and the sides as well) as well as item positioning on toolbars. If you have a legitimately extensive set of first-tier options your GUI should allow users to add/remove command icon+text buttons and even change individual toolbar button displays (icons only, text only and icon+text). A true UX master power user who extensively uses their own application not only is able to satisfy their own needs with a GUI though is also able to completely satisfy another true UX master power user who extensively the first UX master's application.
Being that you're on mobile and that you'll have lots of different options I recommend checking out the Android Nova Launcher, it's a good example of GUI customization and emulating it is a great idea.
Furthermore you should consider finger/thumb target area. Some people have fat fingers/thumbs, some have skinny fingers/thumbs and some people have nails long enough that they could impale and kill Godzilla in a single strike.
Lastly never underestimate the person who customizes the GUI in a way that makes you want to slap them. Presuming that they of their own healthy volition chose certain settings it is key to remember: they're using your application, not someone else's. Use these end-cases to ensure that when you do major updates that you don't frigin break everything! There is an article somewhere on the web that shows user customization that completely break every time they upgraded Windows from version 1.0 and onwards.
So in summary:
- New UX designers should not over-commit until they comprehend long term UI hierarchy.
- Experienced UX designers minimize UX disruptions with new versions.
- Master UX designers eliminate UX disruptions with new versions.
- Icon + Text for your menus by default.
- Icon above or icon to the left is subjective to the screen aspect ratio.