Besides the selling and buying price differences , what else do I have concern of ? The selling price differ for each bank even at the same time . Don't they follow global gold price ?

Eg: -
CIMB Gold Deposit 169.800 164.200
UOB Gold Savings Account 166.90 164.90

Selling price are RM2.90 per gram yet buying price more or less the same. How to choose which bank to invest in ?