Which kind of grip is best during putting?

The best putting grip is one that is most comfortable for you. The most common technique used worldwide is the conventional grip (otherwise known as reverse overlap), but that does not mean it is the one you should use.

Explanation:

It doesnt matter what kind of grip it is, its whatever one is most comfortable for you, like if you have all your fingers comfortably on the grip, then that is the best one for you. But without the right comfort, then it is not usually the best one for you.