My advice would be to start trying things out. We can tell you this and that, but your definition of a good smooth tire is subjective to your perceptions.
So far I have not really been disappointed by anything. I read a little and then make a choice. Continental makes some great tires. Michelin and Panaracer do as well. Lots of folks like Vittorias and Veloflex in one flavor or another. I personally would never choose a Gatorskin, but they are plenty popular. I have 25mm GP5000 and think they are extraordinary. Some disagree.
The internet will give you information, but can't really tell you what you like. No teacher like experience.