Jill, Corniglia is wonderful as Kathy says. A friend was just in the Cinque Terre last week and it was still busy with tourists. Corniglia might be less busy, especially in the evenings, because it is harder to get to.
Expect a lot of tourists on the main hiking trails. If you want some alternate hiking trails, try the one from Manarola to Corniglia via Volastra - it's a steep hike up, up, up! a bunch of steps, but otherwise it's not a difficult hike if you pace yourself. It's not without other hikers but should be far less busy than the main trails between Corniglia and Vernazza, Vernazza and Monterosso. The big payoff from this hike is that the views down are stunning - the best of any of the Cinque Terre hikes I've done.
The hike from Levanto (where I've always stayed, one village north of Monterosso) back to Monterosso is about 2.5 hours and also much less busy than the others.
Neither of the hikes I mention require a hiking pass FYI - or didn't in 2019.
If you want something less busy than the Cinque Terre, try further north in the Riviera. The town of Camogli is a delightful little seaside town, more of an Italian vacation town that gets busy in summer but not so much off season. There are hiking opportunities up there too on the Portofinio peninsula, with far, far few tourists.