Smartphones with touchscreens have been all the rage since the release of the iPhone. So how does it measure up against some recent competition? That's the question recently answered, in part, by MOTO labs, which compared Apple's handset against the likes of HTC's Droid Eris and the Google-branded Nexus One.

MOTO labs, which has developed products that use capacitive touch technology, concluded: "All touchscreens are not created not equal." It used a drawing app to compare the screens on the three smartphones:

On a good touchscreen, users can draw clean straight lines, even while going very slowly, so the graphics that appear on screen accurately represent what was physically drawn.

On inferior touchscreens, it's basically impossible to draw straight lines. Instead, the lines look jagged or zig-zag, no matter how slowly you go, because the sensor size is too big, the touch-sampling rate is too low, and/or the algorithms that convert gestures into images are too non-linear to faithfully represent user inputs.

Also, even on a single device, the amount of pressure and the part of the finger you use on the screen has an impact on how well it senses. A good touchscreen device will produce linear output regardless of whether you're using the full pad of your finger, or just the dry corner of your cuticle. When comparing devices, make sure to use even pressure across all of them.

If you want to show the most extreme case, draw very lightly with the corner of your finger. The artifacts will increase significantly, showing which device is really the best with a weak signal. This is important because quick keyboard use and light flicks on the screen really push the limits of the touch panel's ability to sense.

Overall, the iPhone performed best (check out image for summary of results). See here to learn more and watch a video of the tests of the three smartphones at MOTO labs.