The simplest answer is "any of them".
A more complex answer is "depending on your skill level and how much you want to bother"

Let's assume limited skill so to make this reply possibly useful for as many people as possible.

The best part is that most distro nowadays are available as #LiveDistribution so you can put them on a USB stick and try them to see if you like them and they work well on your system, no strings attached.

The most popular answer is usually #LinuxMint: it's widely used, widely supported and available with an official Xfce version.
#Xfce is a #DesktopEnvironment (henceforth: DE), what manages the actual program windows(to simplify a bit), made with older systems(think Windows7 and older) in mind so less bell&whistles but lighter on CPU and RAM.
You can change it to a "cooler" one(i.e.: #GNOME, #KDE, #Cinnamon, #Mate) later anyway if you want: this is only the "starting look" so to say, to minimize\simplify impact.
Do note Mint is derived from #Ubuntu, with a number of changes(generally taken as improvements), and Ubuntu has been taking decision not everybody like(a #Debian based version is also available).

Another option is #OpenSUSE, currently enjoying a bit of extra popularity due it being developed mostly in the #EU and not derived from other pre-existing distributions. Multiple DEs are available at installation.

#Debian, with its Stable version, is THE paragon when talking about long term stability at cost of using older version of programs. You can manually install more recent ones but that increase the complexity perhaps beyond the scope of the request.
I haven't installed it in decade but I recall the installer not being the most user-friendly. Of course things can have changed wildly since then.

If you dislike having an invasive service manager, you can try out #AntiX, #MXLinux or #Devuan.
...but that might be beyond the complexity limit scope of the request.
Note: MX Linux and Devuan are specifically derived from Debian Stable.