Berkshire Hathaway (BRK.A -0.76%) (BRK.B -0.69%) stock has risen close to 9% year to date. That's not bad, but it's well below the S&P 500's 14% gain.

Warren Buffett had plenty of much bigger winners, though. Here are the three best Buffett stocks from the first half of 2023.

1. Nu Holdings

There isn't any question about Buffett's top performer over the first six months of the year. Nu Holdings (NU 1.66%) stock skyrocketed more than 90%.

Nu runs one of the largest digital financial services platforms in the world. The company serves close to 75 million customers in Brazil, Colombia, and Mexico. 

The fintech stock really began to take off beginning in late March after Nu announced its 2022 fourth-quarter results. Nu reported earnings of $58 million, its second consecutive quarter of profitability. Its revenue totaled $1.45 billion in Q4 -- a record high. 

2. Mitsubishi 

Buffett has become a big fan of five Japanese stocks over the last couple of years. He recently added to Berkshire's positions in all of them. 

Mitsubishi  (MSBHF 0.55%) ranks as the biggest winner of the bunch so far in 2023. Its shares have soared close to 53%.

Like other Japanese trading houses, Mitsubishi is involved in a wide range of businesses. It operates in industries including automotive, energy, food, industrial materials, mineral resources, and real estate.

Mitsubishi's results for its fiscal year ending March 31 provided a nice catalyst for the stock. The company posted record-high earnings for the second year in a row and announced stock buybacks of up to 200 billion yen.

3. Amazon

Amazon (AMZN 3.43%) ended the first half of 2023 as Buffett's third-biggest winner. But it ran neck-and-neck with No. 2 Mitsubishi with a gain of 52%.

Unlike the two top performers, Amazon gave investors something to worry about with its latest quarterly update. Growth for the company's Amazon Web Services (AWS) unit slowed in the first quarter of 2023. AWS usually stands out as Amazon's biggest growth driver. 

But the stock vaulted higher anyway for one primary reason: investors' fervor over the promise of artificial intelligence (AI). Amazon announced multiple new AI tools for AWS customers in April.

Are they buys now?

At first glance, Nu's valuation might seem prohibitive. The stock trades at nearly 48 times forward earnings. However, I really like Nu's prospects in the Latin American fintech market. My view is that this stock will grow enough to justify its valuation.

I think Mitsubishi is a good pick for different reasons. Don't expect jaw-dropping growth from the company. However, Mitsubishi generated strong and steady cash flow. It offers a nice dividend that yields over 3%. And the stock is cheap with an earnings multiple of around 8x.

Amazon might seem absurdly overpriced with its shares trading at 73.5 times forward earnings. But you can pretty much throw earnings-based valuation metrics out the window with the stock because Amazon has historically invested so heavily in growth.

I predict that the adoption of AI and the move to the cloud will provide massive tailwinds for AWS. I look for Amazon's profitability to improve significantly as well. 

In short, my view is that all three of these high-flying Buffett stocks are good picks to buy right now. It's possible that any or all of them could take a breather after their impressive runs. However, Nu, Mitsubishi, and Amazon should be attractive to long-term investors.