Best practice: Install for all users or only current user? I only have one account (and will never get more accounts) on my Mac.

However you often have to choose between installing stuff in /Library or ~/Library.

What's the best practice?

Does it make any difference for me?
It really doesn't make any difference. The vast majority of apps you will ever use will install in a different location (root Library, or user Library), but their configuration will always be user specific.

If you never intend to have other users on the system, the only difference will be remembering where something is installed when you go to delete it.