Branded(Pre-built) PCs Vs. Assembled(Custom) PCs

Branded PCs cost you a little bit more than the assembled PCs. Assembled PCs are good when they're built with quality OEM components and perform equally compared to branded PCs. If you know how to build a PC, you can build yourself and it's easy and you probably saving some money when you build a PC yourself. 
As the branded PCs are sold by the companies like Apple, Dell, Asus, HP, etc.,  The customers are provided the onsite support or troubleshooting by customer care support. 
Assembled PCs are provided support by a local computer seller or if you build the PC yourself, you claim the warranty from the sellers who sold you the components.

Many opt for assembled PCs as they can be built for low cost, and customized configuration.
If you want to build or get a computer built, opt for the Asus, Gigabyte, MSI, ASRock, and EVGA motherboards.
Seagate and Western Digital Hard disks / SSDs are good.
Cooler Master, Corsair, EVGA, SeaSonic, Thermaltake, Antec, etc power supply units are preferable. 
Corsair, HyperX, G.Skill, ADATA, etc. Memory brands are good.
Intel Processors are better but the AMD Ryzen launched affordable quad-core processors with better in-built graphics.