>>>Hi,
>>>
>>>I bought a new PC (window 10). And I will be installing on the new laptop all (important) software I have on my Windows 7. The first thing I will need is a SQL Server Express. Right now, the Windows 7, has SQL Server 2008. I am pretty sure that this is already outdated. What version (year) do you recommend? I have to be careful to install something that will be compatible with the customers' SQL. As far as I know some customers still use SQL Server 2016. Should I get 2014 or go for 2016?
>>>
>>>TIA
>>
>>If they have 2016 you should use 2016.
>>Otherwise you can not get any data from them.
>>And BTW you can have SQL Server Developer edition instead of Express one.
>
>First, thank you for the reply.
>I understand the SQL Server Developer is not free (unlike SQL Express). Am I wrong? And what are the differences between the two versions?

It is free.
Developer edition is Enterprise edition so you can test everything.