The product cycle for the Galaxy S and Galaxy Note are totally different. The new Note tends to arrive in the summer, while the Galaxy S is usually sold just after Mobile World Congress in March. That means that the Note 4 is a slightly more advanced phone than the Galaxy S5. It's also a bit more expensive.
Screen
But the most striking difference between the two is size. The Samsung Galaxy Note 4 is larger at 5.7-inches, while the Samsung Galaxy S5 is 5.1-inches. The Note has a higher resolution too, opting for quad-HD at 1440 x 2560 while the S5 has a 1080 x 1920 full-HD screen. Don't forget too that the Note range has the S Pen, a versatile tool that allows you to write or draw on the screen, and also has the ability to turn your handwriting into text too.
Operating system
Both phones run KitKat out of the box, but both are also in-line to get an update to Android Lollipop at some point in the future. It's not totally clear when this will happen as yet, but the phones will let you know when you can download the new version.
Performance
In the UK, the Note 4 is offered with a Qualcomm Snapdragon 805 chipset, in some countries it's powered by Samsung's own Exynos chips. The S5 uses a slightly less powerful Snapdragon 801, but the differences between the two are pretty small. The Note has 3GB of RAM, while the S5 has 2G, but both are powerful enough to make using apps a smooth and enjoyable experience. The Samsung TouchWiz interface is also improving constantly too, and is a lot faster these days than it used to be.
Internal storage
Internal storage on the Note is 32GB, and the S5 comes in 16 and 32GB versions. Both phones can also accept a 128GB microSD card for storing photos, music and videos.
S health app
Both phones are also aimed at those keen on fitness. Both have a heart-rate monitor but the Note 4 ads a UV sensor to detect levels of ultraviolet from the sun, and a blood oxygen monitor. Samsung ties these features into its excellent S health app, which is also able to monitor your steps and gives you a way to keep track of diet and other things. It's a really good selling point for the Galaxy range, and it sets it apart from other brands.
Camera
The camera is excellent in both these phones too. The Note 4 adds optical image stabilisation too, which should help get crisp shots in low light. Both take 16-megapixel stills though, and both offer 4K video recording at 30 frames per second, and 1080p at 60 frames per second. If you want slow-motion, then there's also a 720p shooting mode at up to 120fps.
Speed
Speed freaks will be pleased to know that, at least in theory, the Note 4 can download twice as fast on 4G as the S5 can. Even so, the S5 offers 150mbps to the Note's 300mbps. Nether is sluggish, and mobile networks aren't yet offering speeds this high anyway.
Conclusion
So, which to buy? If size is an issue, and you need a smaller phone then the S5 offers many of the same features as the Note 4, but in a more compact form factor. That said, the Note 4 isn't that much bigger overall, and offers some really terrific advantages over the S5. The S Pen is great, and the phone's more luxurious metal construction feels more sturdy. The Note is the better phone, but the Galaxy S5 is still a great handset.