The S&P 500 (^GSPC) is home to the biggest and most well-known companies in the market, making it a go-to index for investors seeking stability. But not all large-cap stocks are created equal - some are struggling with slowing growth, declining margins, or increased competition.

Picking the right S&P 500 stocks requires more than just buying big names, and that’s where StockStory comes in. That said, here is one S&P 500 stock that is positioned to outperform and two that could be in trouble.

Two Stocks to Sell:

onsemi (ON)

Market Cap: $24.1 billion

Spun out of Motorola in 1999 and built through a series of acquisitions, onsemi (NASDAQ: ON) is a global provider of analog chips specializing in autos, industrial applications, and power management in cloud data centers.

Why Is ON Not Exciting?

1. Sales tumbled by 13.9% annually over the last two years, showing market trends are working against its favor during this cycle
2. Demand will likely be weak over the next 12 months as Wall Street expects flat revenue
3. Competitive supply chain dynamics and steep production costs are reflected in its low gross margin of 41.2%

At $59.80 per share, onsemi trades at 23x forward P/E. Dive into our free research report to see why there are better opportunities than ON.

Genuine Parts (GPC)

Market Cap: $19.33 billion

Largely targeting the professional customer, Genuine Parts (NYSE: GPC) sells auto and industrial parts such as batteries, belts, bearings, and machine fluids.

Why Are We Cautious About GPC?

1. Sizable revenue base leads to growth challenges as its 4% annual revenue increases over the last three years fell short of other consumer retail companies
2. Disappointing same-store sales over the past two years show customers aren’t responding well to its product selection and store experience
3. Free cash flow margin shrank by 3.3 percentage points over the last year, suggesting the company is consuming more capital to stay competitive

Genuine Parts is trading at $135.49 per share, or 16.8x forward P/E. Check out our free in-depth research report to learn more about why GPC doesn’t pass our bar.

One Stock to Buy:

Comfort Systems (FIX)

Market Cap: $40.19 billion

Formed through the merger of 12 companies, Comfort Systems (NYSE: FIX) provides mechanical and electrical contracting services.

Why Will FIX Outperform?

1. Average backlog growth of 33.6% over the past two years shows it has a steady sales pipeline that will drive future orders
2. Share repurchases have amplified shareholder returns as its annual earnings per share growth of 74.2% exceeded its revenue gains over the last two years
3. Improving returns on capital reflect management’s ability to monetize investments

Comfort Systems’s stock price of $1,150 implies a valuation ratio of 39.6x forward P/E. Is now a good time to buy? Find out in our full research report, it’s free.

High-Quality Stocks for All Market Conditions

Check out the high-quality names we’ve flagged in our Top 6 Stocks for this week. This is a curated list of our High Quality stocks that have generated a market-beating return of 244% over the last five years (as of June 30, 2025).

Stocks that made our list in 2020 include now familiar names such as Nvidia (+1,326% between June 2020 and June 2025) as well as under-the-radar businesses like the once-micro-cap company Kadant (+351% five-year return). Find your next big winner with StockStory today.