One of the biggest leaps in the Galaxy S20 phones over the Galaxy S10 series is 5G connectivity, which theoretically means faster data speeds for streaming videos, video calling, cloud gaming, and faster internet in general. With that said, I wouldn't be doing my job properly if I didn't mention that 5G networks are somewhat sparse at the moment.
Only T-Mobile has a wide-reaching 5G network, covering significantly more Americans than Verizon's or AT&T's. And to note, T-Mobile's 5G network so far isn't the type of 5G that can achieve those crazy gigabit speeds you've heard about, but it is the type with the longest range. Meanwhile, AT&T's and Verizon's 5G networks are capable of impressive speeds, but they have the shortest range.
Still, while 5G networks might not be widely accessible today, they 5G coverage will surely expand over the course of the Galaxy S20 series lifetime. If any form of 5G is available in your area now, or should you want to be ready for it when it comes, you'll be ready with the Galaxy S20 series.
Another quick note: Only the Galaxy S20 Plus and S20 Ultra can connect to those super-fast 5G networks — called "mmWave" — that can achieve those crazy gigabit speeds. The regular Galaxy S20 can "only" connect to the "slower" 5G networks that have greater range. I put those words in quotation marks because it's still pretty great that the Galaxy S20 can connect to a 5G network.