Ok, Here's my March 2017 drone buying guide...
First decide what you want to do with a drone. The decide how much time you're prepared to put into building one, and finally decide how much money you want to spend.
Drones can do a lot of different things these days, but the most popular (in order of popularity) are.
1/ Aerial Photography 70%
2/ FPV Racing 20%
3/ RC flying 9%
4/ Robotics development 1%
The DJI Phantom is the most famous drone in the world. Its the bulbous white one with the squared hoop legs. They're upto version 4 and are really rather sophisticated now. The main things you want in an aerial photography drone are a Gimble (to stabilize your camera), and GPS to make flying easy. The last generation ones are usually heavily discounted so they're a good option if you see them on sale.
DJI have a couple of new drones above and below the phantom that are pretty amazing. The Inspire is really for pro-sumers and costs about 2 grand, and the DJI Mavic is basically a pocketable version of the phantom, and frankly the most bond gadget device that's ever been real. If you're into aerial photography and can afford a Mavic.. get one. They go for about a grand £
There's a million clones of DJIs products, costing as little as 150 quid. They're all a few years behind the phantom, but have basic GPS and waypointing, and some even have ok gimbals. If you want to experiment without spending too much money https://hobbyking.com/en_us/quanum-nova-fpv-gps-waypoint-quadcopter-mode-2-ready-to-fly-1.html are a good option. Once you crash them though they're not really repairable.
If you want to build your own, there's basically infinte options. Before there were really good off the shelf options people were capturing amazing footage like https://vimeo.com/70365435 on home built drones. Get a good frame, choose the right size props, motors, battery. chuck an ardupilot flight computer on it and with a bit of tweaking basically anything can be made to fly.. (this is how i got started.)
This is what all the cool kids are doing. The sports evolving really quickly, but basically everyones settled on a couple of standards: The 250 mini quad (250mm corner to corner) and the tinywhoop ducted indoor quad. If you want a cheap and good off the shelf 250mm racing quad. The wizard x220 http://www.banggood.com/Eachine-Wizard-X220-FPV-Racing-Drone-Blheli_S-F3-6DOF-2205-2300KV-Motors-5_8G-48CH-200MW-VTX-ARF-p-1085802.html?rmmds=search is a great starter FPV racer. You'll need to add a controller, either a Taranis (best http://www.banggood.com/FrSky-ACCST-Taranis-Q-X7-2_4GHz-16CH-Transmitter-White-Black-p-1112717.html?rmmds=search) or a Turnigy Evolution (https://hobbyking.com/en_us/fpv-racer-radio-mode-2-white.html) Nothing else is worth getting. You'll also need FPV googles. Most people start with cheapish Foam box+ screen type googles, and then eventually graduate to expensive Fatshark Dominators https://hobbyking.com/en_us/fpv-aerial-video-telemetry-1/fpv-1/goggles.html The fun thing about FPV racing, is once you've paid for the transmitter and the googles, the quads are really cheap.. These little indoor ones are amazing fun http://www.banggood.com/Eachine-Tiny-QX95-95mm-Micro-FPV-LED-Racing-Quadcopter-Based-On-F3-EVO-Brushed-Flight-Controller-p-1085818.html?rmmds=search
This is where you just fly the quad for fun. Its basically like being telekinetic after a while you get a real rush from being connected to a machine. Everyone that joins monzo gets one of these http://www.banggood.com/Eachine-E010-Mini-2_4G-4CH-6-Axis-Headless-Mode-RC-Quadcopter-RTF-p-1066972.html?rmmds=search After that you basically build one and learn to fly like this: https://www.youtube.com/watch?v=UJ0o05-ULkM
If you want to experiment with autonoumous flight, or develop your own code/algos it's worth knowing about the various FOSS projects. In The Begining There Was MultiWii, literally multirotors were made by attaching 2 wii controllers at right angles to arduinos. Most FOSS projects are somehow descended from MultiWii. For racing drones, the current state of the art is CleanFlight, and its more bleeding edge counterpart BetaFlight (and Raceflight for pros) For waypointing and long distance flight there's a choice, you can go the Ardupilot (aka APM) route, or the OpenPilot (and its descendent Dronin). The code's all 8bit embedded C There's also some new controllers that run on Raspberry Pi's, and some experimental stuff that uses the DSP on a qualcom board (running linux, but the DSP part is realtime so you don't crash when GCing)