What is the best method for date of birth selector?
I want to know what is the most usable and problem free solution, so user wont be confused at all.
If your goal is to make sure "the user won't be confused at all," I think this is the best option.
I wouldn't recommend a datepicker for date of birth. First you have to browse to the year (click, click, click…), then to the month (click some more), and then find and click the tiny number on a grid.
Datepickers are useful when you don't know the exact date off the top of your head, e.g. you're planning a trip for the second week of February.