“Best” is matter of opinion. I happen to like Linux Mint
According to many references it is the most popular, especially for Windows converts. The desktop is very similar to classic Windows.
An advantage is that because it is so popular there is a very large user community which means it is likely you will find lots of help and answers on the forums.
Some people will say ZorinOS is better for beginners from Windows. I tried it a few years ago and it was OK but I found the documentation was a little lacking at that time. I have not looked at it recently.
When comparing Zorin OS vs Linux Mint, the Slant community recommends Linux Mint for most people.
As to the question “What are the best Linux distributions for desktops?” Linux Mint is ranked 5th while Zorin OS* is ranked 39th.
The 4 distributions ranked above Mint (Debian, Slackware, Arch, and Salix) are definitely not suitable for beginners coming from Windows.
6 Best Linux Distributions for Beginners in 2019 rates only Ubuntu above Mint, primarily because it “has great documentation and community support.” But I think Mint is better because all the the desktop environments (Cinnamon, Mate, and XFCE) are a lot more like classic Windows. And XFCE in particular is very lightweight so it runs well on older hardware.
Mint is based on Ubuntu so aside from differences in the desktop environments it is almost the same. Software written for Ubuntu also works on Mint.
I have converted computers for many customers. Mostly old Vista and a few old XP computers to Mint XFCE because it is the most lightweight Mint distribution. Most have had no problem making the transition.
On the same hardware Mint XFCE is faster than Vista and much faster than Windows 10.
I expect I’ll be doing a bunch more conversions now that Windows 7 will no longer be “supported” by Microsoft. Any Windows 7 PC will have hardware that runs Mint very well.
Mint XFCE uses about 350MB of RAM. Windows 10 uses about1.3GB! Mint Cinnamon uses a little more but I had it on an old Vista laptop with 2GB RAM and it ran fine until the hardware failed.
So yes, Mint would speed up an”old” Windows 8 laptop, especially one that didn’t have much RAM.