Mortgage and collateral are terms that are closely related and are constantly referred to when discussing loans. Collateral acts as an insurance policy for lenders that can be sold to cover losses if the borrower defaults on the loan. A mortgage is a loan that uses a certain type of collateral: real estate. As explained, these two terms are closely related, but quite different from each other.
A mortgage is a type of pledge. Any property, including immovable property, can be pledged, while only immovable property is mortgaged, provided that it remains in the possession of the mortgagor or a third party.
To say with precision that a mortgage or a pledge is better: it is up to you to decide - take into account the entire situation, conditions and features of these contracts.