If there is no "money" involved in the transaction, I will suggest you not to choose Method B, i.e. by way of SPA. (the legal fees, & RPGT will be a lot more compare to Method A)

Stamp duty will be based on the market rate (assessed by LHDN) or SPA price, whichever is higher. Thus, the stamp duty will be same, no matter u transfer by Love and Affection or SPA (as you put a rate lower than market rate).

Method A - no RPGT incurred, because your aunty does not gain any profit from the transaction. But if you plan to sell it within 5 years, then you will need to pay RPGT; after 5 years, the percentage is a lot lower.

Method A legal fees will be based on the market rate accessed by the LHDN.

You can do PA as well, but then, bear in mind that, with the PA, the property is not transferred to your brother yet, is just a power to let your brother control/manage the property. In the future, he still need to pay legal fees for transfer the property also.

** If you need to pay some money to your aunt for the property, your brother can refinance after the property transferred to him (Method A); or obtain loan with the PA.