In overdraft facility, banks deposit up to 75% value of the gold to your savings account. You can use as much as you require and pay interest for the amount use and the interest rate could change after a year or before as per the bank’s rule. 

In regular gold loan, you have a fixed interest rate and loan tenure and you will have pay interest for the entire loan amount. 

Choosing between the two depends on your convenient and how much money you would use for your requirement. Overdraft facility allows you to pay interest only for the amount you have used. However, the interest calculation differs and could be little higher than the regular gold loan