I actually purchased both the Toshiba Z830 and the Asus UX31 so I could decide for myself which one I liked the best. Both come with a 128GB solid-state hard drive and 4GB RAM. The Asus has an i5 processor while the Toshiba (which costs $100-200 less) has an i3 processor. Here's what I liked and what I didn't like:
Appearance
The Asus with its spiral design is gorgeous. The Toshiba is boring gun-metal gray with sharp corners.
Winner: Asus
Weight
The Asus is heavier than the Toshiba by a half-pound. As a result, the Toshiba's display has some flex to it and will wobble if the laptop is bumped. In the end, however, I can deal with this. That half-pound is something I can really feel when I'm carrying the laptop around.
Winner: Toshiba
Speed
The i5 processor in the Asus easily beats the i3 processor in the Toshiba I purchased. Of course, you always have the option of purchasing a Toshiba online with the faster processor.
Winner: Asus
Touchpad
The Asus I purchased came with a Sentelic touchpad. The latest driver (ver. 9177) stinks and results in the mouse jumping all over the place. I finally had to uninstall it and rely on the built-in Windows 7 touchpad driver (which meant I had to give up gestures like scrolling). Newer versions of the UX31 apparently ship with a far improved Elan touchpad. The touchpad on my Toshiba is significantly smaller with shiny chrome buttons that pick up fingerprints but it's so far superior to the Sentelic in terms of its functionality. Furthermore, there's a button just about the Toshiba touchpad that allows you to enable or disable it.
Winner: Toshiba
Keyboard
Too many times, I found I had to hit keys on the Asus multiple times before I got them to register. Not so on the Toshiba. Furthermore, the Toshiba's keyboard is wider which allows it to have dedicated Home, End, PgUp, and PgDn keys on the far right. On the Asus, I have to hold down the FN key. Finally, the Toshiba's keyboard is backlit, a very nice touch.
Winner: Toshiba
Display
The Asus has a gorgeous 1600x900 resolution screen. The Toshiba comes with a commonplace 1366x768 display.
Winner: Asus
Ports
The Toshiba has built-in connections for Ethernet, external VGA monitor, and HDMI. The Asus ships with dongles for Ethernet and VGA but requires you to purchase a micro-HDMI adapter separately. Furthermore, the Toshiba has 1 USB3 port and 2 USB2 ports while the Asus only has 1 and 1. Obviously, the Toshiba wins hands down for its plentiful built-in ports.
Winner: Toshiba
AC Adapter
The Asus AC adapter is small and lovingly designed. The Toshiba adapter is bulky and unwieldy by comparison.
Winner: Asus
System indicator lights
The Toshiba has an entire array of useful indicator lights just below the touchpad. The Asus has a couple spread across the keyboard.
Winner: Toshiba
Accessories
The Asus ships with a padded sleeve. The Toshiba doesn't.
Winner: Asus
Heat and Fan Noise
With an updated BIOS in each machine, heat and fan noise was not a problem for me.
Winner: Tie
Speakers
Both sets of speakers are nice and loud, but the Asus Bang & Olufsen speakers sound better.
Winner: Asus
Battery
The Toshiba edged out the Asus by about an hour or so.
Winner: Toshiba
The Toshiba Z830/Z835 is easily my laptop of choice. Granted, it's slower than the Asus, but not noticeably considering how I plan to use it.