Both phones we're looking at here are premium and although Sony's official price for the Z3 is £549, Clove has it for just £515 which isn't too bad for a brand new smartphone. Read: Sony Xperia Z3 release date, price and specs.
However, because the G3 has been around for six months, it's already reasonable price (£479) is even more reasonable and you can get one for just £379 from Amazon which is quite a big saving in this comparison.
Cheaper isn't necessarily better though, so read on to find out whether the Xperia Z3 can trump the LG G3 in design, hardware and software.
Sony Xperia Z3 vs LG G3 review: Design
Sony has been producing dust- and water devices for a while now and the Xperia Z3 is no exception - in fact, at IP68, it has the highest rating yet. This is a big advantage for some users and is something which we are yet to see.
The Xperia range has always been quite big and the Z3 is still a pretty large phone but Sony has trimmed it down to 7.3 mm and 152 g. Its rounded sides make it more comfortable to hold than previously.
Meanwhile, the LG G3 is surprisingly manageable considering its screen size (see below) thank to tiny bezels and a rounded back. At its thickest point, it's a bit bigger than the Z3 at 8.9 mm but it's lighter than its rival at 149 g.
That weight is largely down to the fact Sony uses glass front and back with an aluminium frame while LG uses a plastic rear cover with a metallic skin. Both feel equally premium in the hand.
Sony Xperia Z3 vs LG G3 review: Screen
Sony has made no change on the Z3's screen compared to its predecessor so it has a 5.2in display with a Full HD resolution. It's a great screen at 424ppi and Sony says the reason not to go to Quad HD is partly because it's unnecessary and the negative effect on battery life.
LG was the first to equip a smartphone with a Quad HD display (1440 x 2560) resulting in a 534ppi pixel density. It's something of a debate whether this kind of resolution is worthwhile on a screen this size but we thinks it's incredible and the LG G3 has the best display of any smarthphone.
It's worth noting that although LG has done a great job with tiny bezels, 5.5in is still quite large so some users may find the size difficult to use. In this comparison, it's no harder than the Z3 with its chunky top and bottom bezels, though.
Sony Xperia Z3 vs LG G3 review: Processor and memory
Things are pretty similar here with both phones running on a Qualcomm Snapdragon 801, a quad-core chip clocked at 2.5 GHz. It's a powerful and reliable processor but isn't 64-bit so won't run Android L to its full potential when these handsets are upgraded.
The Xperia Z3 has 3 GB of RAM like theXperia Z2 o but you'll have to but the 32 GB model of the LG G3 to match this as the 16 GB model has 2 GB. LG says the software is designed for 2GB so the extra GB is headroom.
The LG G3 has the advantage of a removable battery and wireless charging. We're impressed with how far the 3000mAh battery goes despite the Quad HD screen lasting us a couple of days which is more than a lot of phones with lower res displays.
Sony has opted to stick with Full HD to offer great battery life, touting two days from the 3100mAh non-removable battery. We've found that it easily lasts this amount of time and will go even further with Son's excellent Stamina mode.
Sony Xperia Z3 vs LG G3 review: Storage
As we've just explained, the LG G3 comes in two storage capacities: 16- or 32 GB. That is at least some choice which Sony doesn't offer because the Z3 only comes in 16 GB. Fortunately, both have a microSD card for adding up to 128 GB additional storage.
Sony Xperia Z3 vs LG G3 review: Wireless
As we've come to expect from 2014 flagship smartphones, the Xperia Z3 and LG G3 come with the latest wireless technology: 11ac dual-band Wi-Fi, NFC, Bluetooth 4.0 and Cat 4 LTE 4G. However, the LG G3 is the only one in this comparison to have an IR blaster and wireless charging.
It's not a big deal but the Z3 uses a nano-SIM while the G3 uses the more common micro-SIM.
Sony Xperia Z3 vs LG G3 review: Unique features
We've already mentioned the G3's IR blaster and wireless charging so that's two unique features with LG boasts and it can also track your steps out-of-the-box.
The Xperia Z3 has the waterproof design (see above) and it also has front facing stereo speakers. Interestingly, both the Xperia Z3 and G3 support playback of High-Res audio although Sony has added support for DSD files making it the first to do so.
Sony's other magic trick is PS4 Remote Play which will arrive in November. This allows PS4 owners to play games on the Xperia Z3 rather than the TV which the console is plugged into. That's a neat feature but only if you own a PS4 or plan on getting one.
Sony Xperia Z3 vs LG G3 review: Cameras
More of the Xperia Z3 hardware is the same as the Z2's with a 20.7 Mp rear camera (you can hardly blame the firm) and it does have improvements in the form of a 28 mm wide angle lens and up to ISO 12800 which is the highest on any smartphone. We also love the dedicated camera/shutter button.
The LG G3's main camera is lower resolution at 13 Mp but it has the advantage of a dual-tone LED flash, a laser auto focus and optical image stabilisation. There's no physical button but you can quick launch the camera from sleep by holding the volume down button.
Both phones can record video in up to 4K quality but the Xperia Z3's SteadyShot with Intelligent Active Mode which keeps video smooth but is only available up to 1080p and 30fps. At the front, both phones can shoot Full HD video but the Xperia Z3 has a little more resolution at 2.2 Mp compared to 2 Mp – no biggy.
Sony Xperia Z3 vs LG G3 review: Software
Both the LG G3 and Xperia Z3 come pre-loaded with Android 4.4 KitKat but Sony keeps things simpler with its user interface.
The Xperia Z3's overlay is close to vanilla Android but with a lick of Sony paint. It's easy to use and stylish and as we mentioned earlier, will get PS4 Remote Play soon. There are a few pre-loaded apps including Kobo, AVG AntiVirus, Garmin Navigation and Vine. Sony has also added the optional feature to double tap the screen to switch it on (not off) which is incidentally something which we first saw on the LG G2.
While LG's is recognisable as Android, the firm has done a lot more customisation than Sony. It's still easy to use and looks good too. It has far more built-in features than the Xperia Z3 with LG's range of Q apps (QMemo, QSlide, QVoice and QRemote). You can also run two apps side-by-side, adjust the keyboard size and there are ways of making the large screen easier to use including the ability to reposition the dial pad and an optional navigation button for the notification bar.
While the LG G3 is packed with more features, it's understandable for a simpler setup to be more appealing. This is where personal taste is important.
There's a lot to like about the Xperia Z3 and PS4 owners may find this battle a no brainer thanks to PS4 Remote Play. However, at more than £100 less expensive, the LG G3 is our overall winner with its amazing Quad HD screen, excellent camera and premium build.