DIY is always the best but think of the maintenance. If you're able to handle it, then good. If you are able to diagnose hardware issues, then replacing them is trivial.
Dell imo, is a good choice for its warranty terms and relative stability. I think they're the only one that allows you to change the internal parts and yet still keep warranty for the rest of the system. I've swapped the hdd, video card and ram and they'll still honor the 3 yr warranty.
HP is another choice but they've been lagging behind the rest in the last few years in terms of hardware. Fortunately, they seem well on the way back with the departure of the last CEO. I liked their customer service @ Alexander. Impecable class, no BS straight to the point , lounge type waiting area but that was a few years back.
The main problem these days is software.
On branded PCs, the amount of bloat is insane. Most consumers cannot escape the OS deteriotion due to the amount of software that gets in sooner or later. Branded PCs have the recovery CD that at least gives the end user an easy way to recover. DIY? You either rely on that poor friend of yours to resolve or try to make your own recovery cd.