Which one to choose ?

WHAT IS AN OEM LICENSE?

An OEM license of Windows or Office (from the English acronym of ororiginal Andequipment mmanufacturer) is a type of license that is inextricably linked to a single PC. This basically means that if for one reason or another you no longer want to use that PC, then you will no longer be able to use the same Windows and/or Office product key on the new computer. Furthermore, if you want to change some components on the PC equipped with a Windows OEM license, that same license will probably no longer be able to be used even on the same computer.
In particular, if on the PC equipped with the Windows OEM license you want to change the motherboard, for example, then that same Windows OEM license can no longer be used even on the same PC. Instead, if you make less radical changes, such as changing video cards, changing hard drives or changing/adding RAM memory, in this case, most likely, the Windows OEM license will continue to be valid. Unfortunately, the conditional in these cases is a must as Microsoft is not very precise in this respect, leaving out the fact that every now and then it also makes small changes to the license agreement.

WHAT IS A RETAIL LICENSE?

A retail license of Windows or Office (pronounced ritèil) is a type of license that allows you to install Windows and/or Office on any PC allowing, if necessary, to be moved from one computer to another. In other words, if you decide to change computers, with a retail license you can easily take the version of Windows and/or Office and install it on the new computer without running into any problems. However, this does not mean that you can install the same version of Windows and/or Office at the same time on multiple computers but only that, once Windows and/or Office has been uninstalled from the old PC, that same license can then be used on any other computer without run into any problems.

WHAT IS AN ESD LICENSE?

A license of Windows or Office in ESD version (from the English acronym of Andelectronic ssoftware distribution) is a type of license that Microsoft offers in digital format without the aid of any physical medium (such as the classic box, DVD, user manual, etc.), thus reducing costs due to packaging and shipping . The main advantage of an ESD license is undoubtedly its price
The problem in these cases is not so much from a legal point of view as, as has already been established here by the Court of Justice of the European Union, in Europe and in Italy ESD licenses are perfectly legal, but more than anything else it is to verify the actual usefulness of the Product Key of this type of licence.

WHICH LICENSE SHOULD I BUY?

If you intend to change PC components often or in any case you already know that you want to change computers from time to time by bringing your version of Windows and/or Office from one PC to another, in this case, then, the ideal solution is to buy a retail licence. If, on the other hand, you are among those who don't change computers often, then in this case the OEM license of Windows and/or Office is the right one for you, thus also allowing you to save money. A license of Windows or Office in the OEM version costs much less than the counterpart in the retail version. However, keep in mind that with an OEM version license you will not have direct support from Microsoft, which means, in case there are problems with Windows or Office, that you will not be able to call the Microsoft assistance center to get some support.
Finally, an ESD version Windows or Office license, depending on the case, can be similar to both the OEM license, the retail license, or the MSDN license, in that there is no single version of the ESD license but it depends, more what else, by the seller in question who decides from time to time which of these three licenses to associate with the ESD license.

Although things may change in the future, in principle they should always remain the same, more or less. However, at this point you should finally understand what is the difference between OEM, retail and ESD licensing.