Alienware are the best know brand for gaming laptops however they are all also probably the most overpriced.
MSI and razor do nice gaming laptops, gaming laptops are pretty much pointless though given the power drain for the gpu and cpu during gaming, which means you'll need to have it powered for more than an hours worth of play, you'll need fireproof trousers due to the heat they kickout, you'll want a proper mouse and keyboard to play comfortably. The real reason they exist is so that you can pick them up, take them to LAN parties where you can plug them into a monitor, keyboard and power.
In terms of upgradability, you'll be able to increase the RAM and HDD but 9 times out of 10 the gpu won't be, given how good the cpu's are these days the gpu is the limiting factor in games, for example my cpu will sit around 25% usage whilst gaming, whilst the gpu will be at 80-90% as the graphics are the bottleneck these days, this means once your laptop gpu is outclassed by the game then it's a normal laptop.
unless you have a specific need for a laptop style machine, for gaming a desktop pc is always the best way to go, given how easy it is to upgrade and future proof them, as a guide you can build a pc with an equivalent spec to the ps4 and xbox one for £400-£500