The difference in name between 'RX100' and 'RX100 II' is minor, but when it comes to features and performance the RX100 II is clearly the superior model. Still, with the original RX100 sometimes dropping in price to less than $500 (at the time of thiswriting), it's a good alternative for someone who wants a solid compact camera, but balks at the RX100 II's $700 price tag.
RX100 II connectivity: it's there, but it's not brilliant
The RX100 II offers Wi-Fi support, which lets you upload photos and control the camera from your smartphone. Unfortunately, we found the Wi-Fi interface a little clunky; only one size photo is automatically transferred to your phone, you can't share photos with social networks directly from the camera and the controls available to you from your smartphone are rather limited: shutter, exposure compensation and video recording. So the Mark II does give you Wi-Fi, but it's not a particularly strong implementation.
Accessorize!
The accessory hot shoe is a nice addition, letting you attach an external flash, the fantastic (optional) electronic viewfinder accessory, or an external mic. The tilting LCD is another welcome addition, letting you compose your shots up high or down low. Sony also saw fit to improve video frame rate options, and you get a slightly faster AF with the RX100 II as well.
The main attraction for the Mark II is the greatly improved sensor
But the real draw? That would be the RX100 II's sensor. Sony swapped out the original RX100's sensor for a version using backside illumination (BSI), a technology that greatly improves light sensitivity on sensors of this size and resolution. This gives you roughly an extra stop of performance when it comes to high ISO noise: ISO 3200 on the RX100 II should be as clean as ISO 1600 on the RX100 (you can see for yourself how good it is in the low light comparison section of our review). And of course noise at any given ISO drops significantly. Not content to just raise sensitivity at a given ISO, Sony also increased the maximum ISO from 6400 to 12,800.
Given the price difference, it's something of a toss-up
The RX100 II won our award for the best pocket camera of 2013, and is the superior camera by just about any measure. But is it worth the $150-200 price difference? Our testing didn't see as big an improvement in RAW files as JPEG files (~1/3-1/2 stop vs ~1 stop), so RAW shooters on a tight budget might give careful consideration to the RX100. And those on a budget or those who don't need the latest features might also consider saving their money. That's because the RX100 is a stellar camera -- so good, in fact, that it took the award for best pocket camera of 2012. Despite being nearly 3 years old now, it's arguably the best compact camera available for $500 (again, at time of this writing).
--Tim Barribeau