FORTUNE — No 16 GB smartphone on the market actually delivers 16 GB of usable storage, but some come closer than others.

Of the eight models evaluated by the British product-testing charity Which?, Apple (AAPL)‘s iPhone 5C scored the highest with 12.6 GB (79%) of free memory.

The worst: Samsung’s Galaxy S4, with only 8.56 GB (53.5%).

Where did the other 46.5% go? Which?’s John Barrow thinks he knows:

“Many manufacturers further stuff their phone with pre-loaded apps, skins and bloatware. And no phone has more piping, braiding and frills than the Samsung Galaxy S4.

“Running on Android, Samsung has heavily customised the S4 with their Touchwiz interface. This includes many of Samsung’s own features but, while it looks pretty and grabs headlines, most of the stuff is next to useless. Eye tracking technology that pauses video when you look away from the screen sounds attractive but in reality it works badly, gulps down your battery and monopolises your internal storage.”

On the plus side for Samsung, the Galaxy comes with a Micro SD slot for adding more memory as needed. The iPhone does not; with Apple, what you buy is what you get.

LINK: Phone storage compared – Samsung S4 still in last place