Based on price comparison (best bang for buck, from best to worst)
Aftershock > Alienware > Razer
I will use the 15 inch as a base model of comparison. (17 inch ver. should not differ much)
Razer:
Start off with Razer first. I've nothing against it, I am a Razer fan and have many Razer gaming peripherals - mouse, keyboards, mouse mats and headset, but the laptop is a real no-go.
Firstly, its overpriced, with the cheapest Razer 2015 HD 256GB version priced at SGD 3000. The pricier QHD 256GB version (which can be found in local stores) is tagged at SGD 3599. If you know where to buy (Hint hint Gamepro@funan), you can get it at a few hundred $$ off if you don't want the freebies (gaming mouse/mousepad/headset). Nevertheless, its still the most expensive out of the 3.
Secondly, its specs are the lowest out of all 3 (as of 1 Jan 2016). Razer Blade is running on 4th Gen Intel Core i7 and GTX 970M which is good for a gaming laptop, but can be better with the price tag. It also boasts only an 16GB DDR3 ram instead of DDR4 which is what is mostly found in the market right now. The 2016 version, which might be coming out soon will probably have the latest 6th Gen Intel i7 but will still be tagged at the same, exorbitant price.
Lastly, the form factor. It is a beautiful piece of art, I have to admit. It is so much like a Mac (I am a mac user) and I was so tempted to buy it at one point in time. That, is also what makes this laptop a huge no-go. The cooling system. The Razer Blade can get so overheated that is no joke. It'll definitely get fried if you use it for continuous gaming over the course of a few years. Do a quick google search and you can find everything you need to know about it.
Razer Blade is well, good if you like portability and look stylish, have money to burn. But if you have a budget to keep, nah.
Alienware
Next, up Alienware. My personal favourite and I recently bought the Alienware 15 because of a promotion which I'll be talking about later.
Nothing much to say about this, the top model which has 6th Gen Intel Core i7, 16GB DDR4, GTX 970M is priced at SGD 2799 which is well, abit pricey albeit still within an acceptable margin. It could do better with a GTX 980M with that price but thats what you get for buying for the brand. It does have a good and "cool" form factor though, with customisable keyboard lighting etc. Oh, and it comes with 1 year warranty which covers accidental damage. Means you can spill water on it and get it repaired for free. How nice. The biggest downside and the complain I have with it is the size and weight. Hell, it is HEAVY for a 15 inch laptop, at 3.1kg. It is quite bulky as well and you'll need a big bag. Its justification for it is, good cooling system.
The best part of Alienware is its Graphic Amplifier. Its this gimmick which allows you to house a DESKTOP GPU and connect to your laptop. It also has its own power source so you don't have to worry about your laptop not drawing enough power. So what does it mean? Firstly, it means your laptop can become more of a "desktop" replacement as it is using a desktop GPU and secondly, after 3-4 years and your laptop GPU has degraded, you can still enjoy the same or better performance by buying a desktop GPU and using the Amp. The Amp is priced at SGD 419 and not inclusive of the desktop GPU. I got this for free during the promo and even got 200 off when I said I do not want the freebies when i bought at Gamepro@funan.
Aftershock
Lastly, Aftershock. A truly innovative, cheap and best of all, a local brand which I'll like to support. A lot of my friends have bought from Aftershock and sang praises about it.
Its "maxed out" version of the S-15 (ignoring disk space upgrade, the default is 256GB SSD + 1TB HDD which is sufficient) which is equivalent to the Alienware 15 and Razer Blade 2015, is priced at about 28xx and it features the best specs among all, with 6th Gen Intel i7, 16GB DDR4 and GTX 980M (finally, a 980M)
It is also light, at 2kg and has a smaller form factor. Personally I find the laptop quite plain but there's this option where you can customise the colors etc of your case! It also boasts 3 fan which makes its cooling rather fantastic and you won't feel the laptop getting heated up.
Conclusion:
Get a Razer only if you have the money and don't care about anything else. Its pricey and yet you don't get what you pay for. (Unless you find the form factor is what you are paying for)
As for alienware, its has been cheaper as compared to like 5 years ago, but it still sits between Razer and aftershock. I like it because its looks futuristic, and its stats are quite decent for its price. If you like its looks and are willing to fork out abit more, go for it. Its not as overpriced as Razer.
If you're the a money-minded person and want to make all your $$$ spent worth it, Aftershock is your best bet. You're even doing Singapore a favour by supporting a local brand, so why not?