700c is the standard wheel diameter used on virtually all adult road bikes — if you're shopping for a road bike, you'll see this spec on nearly every model. The "c" is a legacy sizing label, but the important part is that 622mm is the actual bead seat diameter, which is the industry standard for road cycling.
The big advantage of 700c is selection. Because it's the universal standard, you'll have access to the widest range of replacement tires, tubeless setups, and upgrade wheelsets at every price point. Whether you need skinny 25mm race tires or wider 35mm gravel rubber, 700c has you covered.
For the vast majority of road riders — whether you're racing, doing group rides, or logging solo miles — 700c is the right and only choice you need to consider. The only reason to look elsewhere is if you're building a specific all-road setup with very wide tires (47mm+) on a smaller frame, where 650b wheels might come into play.