Costco's (Nasdaq: COST) fiscal first-quarter results once again showed its mettle. Investors should never underestimate this well-run discount giant.

For the quarter, Costco's net income increased 17.3%, to $312 million, or $0.71 per share. Total sales increased 11%, to $18.8 billion.

Same-store sales increased by 7%, and even if you strip out positive effects of gasoline and foreign currencies, comps jumped 5%. The U.S. saw comps increase 4% (ex gas), but international comps surged 10%. The company's membership fee revenue increased 10.3%, to $416 million.

Costco's quarter was a strong victory in a difficult consumer spending environment, one in which major rival Wal-Mart (NYSE: WMT) has experienced trouble generating robust U.S. sales and customer traffic.

Meanwhile, Costco's clearly holding its own against retail rivals that sell similar wares, such as direct warehouse competitors like BJ's Wholesale (NYSE: BJ), discounters like Target (NYSE: TGT), electronics peddlers like Best Buy (NYSE: BBY), and pure-play grocers like Safeway (NYSE: SWY).

Earlier this week, Costco became my second buy for my Rising Stars portfolio, which focuses on socially responsible investing. Costco's a well-run company that keeps all stakeholders in mind, and even though it tends to trade at a premium to rivals, there's a point where long-term shareholders should consider paying a little more for a company that's not only well-positioned for growth, but also provides a prime example of a truly good company one can be proud to own.

Today's quarterly results underline Costco's formidable retail skills to boot; investors shouldn't underestimate its competitive advantages in the marketplace. Underestimating Costco seems like a mistake to me. What do you think? Let us know in the comments box below.

Costco, Best Buy, and Wal-Mart are Motley Fool Inside Value recommendations. Best Buy and Costco are Stock Advisor picks. Wal-Mart is a Global Gains selection. Motley Fool Options has recommended buying calls on Best Buy. The Fool owns shares of Best Buy, Costco, and Wal-Mart. Try any of our Foolish newsletter services free for 30 days.

Alyce Lomax does not own shares of any of the companies mentioned. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.