Are you thinking of buying one of the big four banks for your portfolio?

Deciding which bank to buy ahead of others is not as easy as you think. Especially when they are trading on higher than normal multiples following strong gains over the past 18 months.

The good news is that the team at Macquarie Group Ltd (ASX: MQG) has picked out its favourite from the sector right now to save you from trying to figure it out yourself. Let's find out which one it is.

Which big four bank?

The bank that has been named as Macquarie's favourite is National Australia Bank Ltd (ASX: NAB).

However, that doesn't necessarily mean that investors should be buying its shares. While it may be the broker's favourite in the group, it isn't recommending it to clients just yet.

According to a note out of the investment bank this morning, its analysts have reaffirmed their neutral rating and $35.00 price target on NAB's shares.

This compares unfavourably to the current NAB share price of $36.28 and implies potential downside of 3.5% for investors.

Commenting on its neutral recommendation, the broker said:

NAB is trading at ~16x FY26 P/E and ~1.7x P/B. While still expensive in absolute terms, NAB has the least downside risk to earnings from rate cuts, and balancing execution risk with its valuation profile, NAB remains our preferred exposure to the sector. Maintain Neutral.

What about the others?

Macquarie is bearish on Westpac Banking Corp (ASX: WBC) and has an underperform (sell) rating on its shares with a $27.50 price target.

It thinks Australia's oldest bank's shares are expensive. It said:

WBC remains expensive, trading at ~17x FY26E P/E (6-26% premium to ANZ and NAB). With execution risks around the UNITE program, in addition to headwinds from rate cuts, we continue to see risk to WBC's earnings and multiple. Maintain Underperform.

ANZ Group Holdings Ltd (ASX: ANZ), which released its half year results this morning, is currently rated neutral with a $28.00 price target. Though, this could change when Macquarie has updated its model to reflect the big four bank's results release.

Finally, Commonwealth Bank of Australia (ASX: CBA), which will release its quarterly update next week, is currently rated as underperform by Macquarie with a lowly $105.00 price target. This implies potential downside of approximately 35% for investors.

Though, it is worth remembering that this recommendation could change once Macquarie has seen CBA's update next week.

Overall, investors may want to keep their powder dry and wait for a better entry point with the big four banks.