PC Components

A brief guide on PC Part selection.
Having good specs does not necessarily make a PC part good.
Always read reviews.

Monitors

Go IPS every time. If you're really rich, you can go OLED.
I prefer 4K over 120 Hz but if you can find a good deal on QHD 120 Hz that's good too.
Note that some lower-end GPUS and adapters won't be able to output 4k60.

Peripherals

Main article: Peripherals

PC Parts

Case

These days, you should be able to get one with USB-C.

Heatsinks

The Noctua NH-D15 is one of the best air coolers available. Noctual often sells mounts for new sockets so you should be able to reuse it for several builds. However Noctua coolers are quite expensive. These days, there are now several cheaper dual-tower options like the Scythe Fuma 2 and Thermalright FC140/FS140.

Fans

Typically go with Arctic P12/P14 or Noctua fans.

You can buy 1500-2000 RPM PWM fans and tune down in the UEFI/BIOS.
Typically, several slower fans (600-800 rpm) is quieter than fewer faster fans.

For 3-pin fans, the range of fan speeds is typically much smaller. So try to get fans closer to 1000 rpm if you're going with DC fans.

Motherboards

The most important thing to look for is the VRM quality. Bad VRMs will throttle your CPU even at stock settings and with good cooling.
There are VRM tier lists for most motherboard chipsets.
Here is one for AMD.

Power Supplies

Check the check the PSU Tier List.
For high-end builds (i.e. Nvidia 3090 class builds), pick something in the A-tier section.
Corsair AX/HX/RMx, EVGA Plat/Gold, and Seasonic PSUs tend to be good choices.

In general, these will come with a 10 year warranty and 80+ Gold or better efficiency. If you can find a sale, 80+ Platinum power supplies are even better (e.g. Corsair HX).
Most expensive PSUs will keep the fan off when load is under 40% so try to aim for a high-wattage PSU. Furthermore, higher wattage will be better against GPU spikes.

SSDs

Go with M.2 nvme.
Samsung 970 Evo or 980 Pro are the default safe choices.
Avoid SSDs without DRAM. Check online for specs.

Hard Disks

Avoid for PC and Workstation builds. It's not worth the weight, or noise. See Data Hoarding for how to setup a NAS.

CPUs

Intel or AMD are both fine nowadays.

RAM

I always test RAM, both new and used, upon receiving it with Passmark's Memtest86.
Failing memtest86 means either the ram is bad, your settings are unstable, or your CPU's memory controller isn't good enough for the overclock.
Sometimes, XMP speeds can be good with a small amount of ram but will fail with more ram due to a week memory controller, particularly on earlier Ryzen CPUs.

For XMP overclocked ram, it's best not to mix ram models.
For JEDEC stock ram, it's usually okay to mix models as long as both have the same specs.

In general, you want the highest MHz and the smallest CAS latency.
For Ryzen 3000/5000 and Intel 8-12th gen, only up to DDR4-3200 is officially supported.
For most applications, DDR4 memory speeds have diminishing returns above 3000 MHz so don't spend too much extra.

Used vs New

Things which I prefer to buy used:

• CPUs - very rarely DOA and very rarely goes bad with time. Just make sure there are no bent or missing pins.
• Memory - easy to test with Memtest86, very rarely goes bad with time.
• GPUs - if it's a newer model, it'll typically still have a warranty.

Things I prefer to buy new:

• Cases - to make sure you get all the screws
• Motherboards - to make sure you get accessories like the IO shield
• SSDs and HDDs

If it's part of an entire build, the above used parts are fine to leave in.
Used motherboards are okay if part of a bundle, i.e. with CPU and cooler. Just make sure there are no broken pins.