I've been out of the market for a while now, so I can only give very very general advice. I don't know any of the specifics of any hardware anymore. Take what I say with a grain of salt.
First off, laptops are completely different from desktops, prepare to pay extra for the compact size of a laptop. You're also going to have to pay whatever companies want if you're going that route, because building a laptop just isn't really done.
As far as desktops go:
Alienware is overpriced at every price point. You're paying for a brandname and for their professional designers to model cases—not for function. It's the same for Ibuypower and other similar sites. I haven't looked at these sites in a long time, but I imagine the story is still the same.
Dell used to be really really bad, but there's not much difference between them and other major brands anymore. Some people say that boats are something you buy if you want to watch money sink down a hole really fast. My dad used to say the same about Dell, but the stigma isn't deserved anymore
Some of the very low end Dell Desktop PCs are actually competitively priced with building your own—sans the graphics card which you would still need to purchase. This is true *mostly* because of software prices (which in my opinion are obscene). You'd have to buy an OS anyway, and I think dell computers come with Microsoft Office (if people care about microsoft office anymore).
This gets less and less true as you move up the price range—they too start over charging compared to what it would cost you too build your own.
I would still recommend building one from scratch. http://www.tomshardware.com/
is a good resource to learn about computer parts. https://pcpartpicker.com/
is another resource.
I built mine 8 years ago and its still playing all the games I want it to (at a better framerate than consoles with farther draw distance and other such things). I spent about $1000 on my pc back when I built it and EVERYTHING, as near as I can tell, has only gotten cheaper. I only recently upgraded my graphics card because my old one became legacy hardware and wasn't going to receive any more drivers updates.
Don't skimp on the PSU. Corsair is a good brand for PSU and RAM.
Sapphire is a good brand for Video Cards-great customer service. It's better to have one high end video card than two mediocre SLI'd video cards
Intel is better CPU wise than AMD and has been for a long time now.
An i5 cpu is good enough for the majority of users — most things don't take advantage of hyperthreading yet (so many games still only use one core) so unless you're into sound design you probably aren't looking at getting an i7. Another possible use for hyperthreading is streaming on twitch.tv or whatever.
Get a motherboard that fits the CPU, the RAM, and the videocard. Other considerations include USB ports.
SSDs are a good investment in my opinion. The boot time of your PC will be much faster and then several games that I play would be a massive pain if they weren't on an SSD (such as Path of Exile).
Actual assembly isn't any harder than legos. Just make sure everything is going in the right holes.
The majority of the maintenance for a computer is cleaning the dust out and properly cleaning, then reapplying cooling paste between your CPU and the CPU's fan every 6 months or so. It's not really necessary that often, but it's good to do so.