Long term storage in a desktop computer is most commonly bought through Solid State Drives (SSD) and Hard Disk Drives (HDD). HDD's are cheaper than SSD's and can contain more Data. However HDD's are much slower than SSD's so a HDD doing tasks like booting up windows will take much longer than if an SSD were to do so. When choosing a method of storage for you PC you should think of three things: How much storage do I need? What speed do I need? How much money am I willing to spend?
How much storage depends on what you are planning to do with your PC. If your planning to game on your PC then I would recommend at least 1TB of storage because many modern games require over 100GB of Storage. If your going to just do work like word documents and storing photos then I would recommend at least 500GB of storage. For other things like complex rendering and Video editing I would recommend at least 1TB of storage. I personally have a 1TB Hard Drive and I store a lot of games, photos and work. I have never run out of space on my HDD. But as time goes on and games become more complex and photos get higher resolutions you will need more and more storage so when building a PC I like to try and make it reasonably future-proof as long as the budget allows.
What speed you need is up to you. If you're fine with waiting a few minutes extra for windows to load or for a game to load then a Hard disk drive is for you but if you are happy spending a bit extra to allow the convenience of not waiting several minutes for things to load than an SSD is for you. There are two types of SSD's. SATA SSD's and NVME M.2 SSD'S. NVME SSD's are the fastest but also the more expensive option. An average SSD is approximately 500Mb/s read and write while an average NVME SSD is about 2,000Mb/s read and write. The difference is very noticeable for tasks like video editing, Data Transfer and viewing many high resolution photos at a time. But for things like booting up a game the difference is not noticeable because most games are not designed to load at such high speeds as an NVME SSD. I don't own an SSD as I am fine with turning on my PC and waiting five minutes but I am considering getting an SSD. Also as time goes on and the average file size increases, transfer of Data will need to increase too so getting an SSD will make your Desktop more future-proof.
NVME SSD
Pros: Very high speeds of up to 5,000Mb/s
Cons: Very Expensive
Requires an M.2 NVME PCI-E 3 slot on motherboard
SATA SSD
Pros: High speeds of up to 750Mb/s
reasonable price
uses a SATA slot which majority of motherboards have
Cons: Speeds might not be fast enough for video editing and other storage heavy tasks.
Hard Drive
Pros: Large capacity
Low price
Cons: Slow speeds of up to 150Mb/s
Data can easily be corrupted due to static or physical damage
The 1TB and 2TB Hard Disk Drives from Seagate are pretty good value. I personally have a Seagate 1TB HDD in my PC and it hasn't failed on me. I'd recommend that you use these drives as your secondary Drives to store large files and have a low capacity SSD to store windows and a few applications.
For a SATA SSD I would recommend the 500GB WD Blue SSD. 500GB is plenty for storing windows and a lot of games, files and photos. I'm currently considering buying this SSD for myself . The SSD goes up to 560Mb/s read and 530Mb/s write.
This NVME SSD is quite cheap for 500GB. It's a PCI-E Gen 3 x4 M.2 SSD, so make sure you have an M.2 PCI-E Gen 3 x4 slot in your motherboard. With 500Gb you will be able to store windows, your favourite games and other files. The NVME SSD goes up to 2,000Mb/s read and 1,700Mb/s Write