Is macOS Big Sur better than Catalina? That largely depends on what hardware you're running, because some older Macs are not supported. To run Big Sur you'll need one of these Macs:
MacBook (2015 and later)
MacBook Air (2013 and later)
MacBook Pro (2013 and later)
iMac Pro (2017)
iMac (2014 and later)
Mac Mini (2014 and later)
Mac Pro (2013 and later)
Anything older and you're out of luck. You'll also need 35.5GB of storage space to install the upgrade.
macOS Big Sur isn't the most recent Apple operating system: that's currently macOS Monterey, which was released in late 2021. Generally speaking, if your Mac is capable of running Big Sur then it's also capable of running Monterey, and that's the Apple OS we'd recommend most. Apple has a hardware compatibility list for Monterey here (opens in new tab).
Back to our original question: is Big Sur better than Catalina? I think it is, with some important caveats. The interface is quite dramatically different and much closer to iOS/iPadOS than before. System Preferences has been overhauled in lots of areas such as the Battery screen, and the Notification Centre and revised menu bar are quite different too. There's also a lot more space in Big Sur, so if you prefer your operating system to be as small as possible you might not like it.
There aren't a lot of huge app updates but the improvements to Maps, Books and Mail are welcome. Safari is better too. And the biggest app change was a really big deal: Big Sur could run iOS apps, albeit only on Macs powered by Apple silicon.
The most important difference, though, is security and privacy. Safari's privacy protection is much better, and Big Sur introduced a new Signed System Volume to protect you from malicious software.
On balance, I'd say Big Sur is better than Catalina – but I also think Monterey is better than Big Sur, so if your Mac can run it that's the one to get.