A premade is likely to cost less, unless you highly customize and deviate from their standard builds. This is because the big PC makers can go to Western Digital and buy 100,000 hard drives, at considerably deep wholesale/volume discounts. Or to Intel and buy 200,000 CPUs. Or go to Microsoft and buy 1,000,000 Windows licenses. Individual builders cannot buy at bulk, warehouse prices.
A premade will have 1 phone number for all maintenance and tech support. And that's a significant advantage and one you must consider. Self build, you're it. Another advantage to the big guys is one stop shop for all your hardware drivers. Not sure about your EasyPC place, as they seem more like custom PC builders than mass production builders like Dell, Acer and HP. It looks like with them, its up to you.
My philosophy as a self-builder centers around my acceptance that I cannot compete in price with Dell, Acer, HP or the other big makers - but I can build a better computer in any category. Why? Because I can pick and choose the right parts (READ: distribute the budget) for the specific user and anticipated usage.
PC "builder" is a poor, way over-used term - though I am not sure of a better one. "Building" a computer is a one, or two step process - depending how you look at it. I see it as two.
1. You "assemble" the parts. Really, how hard is that? It is not. One #2 Phillips screwdriver. There are just a few precautions (ESD control is essential, proper case standoff placement is critical, as is proper application of TIM). But these are easily mastered, with a little patience, a steady hand, and a strategic placement of tongue. Technically, once "assembled" and wired, you have a computer - but at this point, it is just a big power consuming, heat generating paper weight.
2. It becomes a "personal computer" after you setup the drives/partitions, install an OS, install and setup security, install specialized drivers, setup networking, install and setup productivity software.
If you feel your computer is just another communications "appliance" in the house, then buying a prebuilt is probably better. But if you want to "learn" and understand how the various parts of a computer, and more importantly, your
computer fit together (literally and figuratively), then building your own is the best way.
While building your own may cost more from the start, careful and strategic planning can end up saving you money in the long run. You will be able to upgrade your computer in steps over the years so it evolves over time to stay relatively current. This is a lot cheaper than paying for a whole new computer every few years.
While most pre-builts can be upgraded too, options may be limited, and certainly you would not have the experience or knowledge you would have got from assembling it yourself. If you put your own computer together, you would probably not hesitate to, for example, add a couple more sticks of RAM yourself, if you wanted. Or replace the battery. And you would feel much more comfortable giving the interior a good cleaning of the heat trapping dust that WILL accumulate, if not regularly cleaned.
If you are interested in learning about any of those things, about feeling confident while digging around inside that you will not make things worse, then hands-on is by far the best.
Something else to consider, now that I look a little closer at those EasyPC specs. EasyPC warranties the computer for 1 year. My concern is the CPU warranty. Both Intel and AMD warranty their "retail" versions of CPUs that come with OEM supplied coolers for 3 years. The warranties specify that using 3rd party coolers and overclocking violate the terms of the warranties.
That EasyPC uses a 3rd party cooler and overclocks the system. If that extra 2 years of CPU warranty is not a concern to you, then no big deal. But thought I would point that out.