IDK that you will ever get people to agree on a 1 best. There are many to choose from, I’d say read HKJ’s reviews and go from there. General rule is to buy good quailty cells from a reputable dealer. I’d stay away from most “**Fire” brands and Ebay is notorious for fakes. If you don’t want or need protected cells I really like using laptop pulls.
Below are couple of my favorites. Efast are good too.