We were in Riomaggiore for 3 nights.
We walked to Trattoria Dal Billy in Manarola 2 nights! It was wonderful! Both nights we ordered the mixed seafood antipasto. Not only was it delicious, it was never ending. They keep bringing you small plates of seafood & other treats. I think we had 12. The first night we were not expecting it, so we were very amused as they kept bringing more & stacking them on our small table (we didn't have reservation, so we were lucky to get a table at all). The second night we made a reservation & got a bigger table. The whole fish w/potatoes is great & so is the shrimp pasta. It is quite a hike, especially from Riomaggiore, but the food & the view are worth it. And, you get limoncello, grappa & mirto (which is fantastic!) at the end of the meal.
The only other dinner we had was at La Grotta in Riomaggiore. It was very good. We split a huge earthenware bowl of mixed seafood for our primi & should have stopped there. Not because the pesto & fish we had later were not great, but because it was HUGE! We went back for lunch the next day & split a Caprese & the best calamari we have ever tasted. It was one of the best lunches we had on our trip.
We didn't spend enough time in the other towns to eat much more than gelato, but I would have taken the train from any one of them to eat at Billy's.