Release for Pi Day 2018 (3/14/2018), the upgrade to the perennial favorite has a new, slightly faster 1.4 GHz Cortex A53 four-core microprocessor, new Wi-Fi chip (2.4 and 5 GHz now possible), and Gigabit Ethernet, as well as PoE. Heat shield over the CPU as well as better temperature monitoring allowed for the speed/cycle increase as well as clock management. Also has PXE management and USB mass storage booting (yes, you can boot over USB). More details here: https://www.raspberrypi.org/blog/raspberry-pi-3-model-bplus-sale-now-35/
Pro World-class support and software
What really sets the Raspberry Pi apart from the competition, and makes it leagues apart from every other SBC out there, it the software and support you get from every corner of the ecosystem regarding anything you want to make, build or do with the Pi. The most up-to-date kernels, the widest supported bundles, hats for every occasion, step-by-step instructions, and if you're trying something and get stuck, chances are high someone else has got stuck at the same spot, got past it, and left detailed instructions on how to get past it so nobody ever gets stuck there again. That is the best feature of the Raspberry Pi.
Pro Faster networking capabilities
Because of the Gigabit ethernet (although still sharing the USB 2.0 bus which limits its speed ceiling), it goes up to 3x faster than the original Pi 3 Model B. The new wireless chip supports 802.111ac, which also increases its throughput to 3x as well. Bluetooth 4.2 LE is much more stable, and it's just a nice little upgrade.
Pro Faster CPU than the original Pi 3 Model B
Thanks to a new thermal management plate (heat spreader), as well as better voltage regulation, the CPU gained a nice little 200 MHz bump in clock speed over the Pi 3 Model B. Applications on the Pi 3 B+ are a little faster and snappier than their predecessor.