It's summertime and the stock market is sizzling.The market reached an all-time high this week, torching its previous record set just before Memorial Day.Even so, a handful of companies stand out. Six stocks - Amazon, Starbucks, UnitedHealth, Visa, Mastercard, and Discover Financial - notched their own records this week, helped by the growing confidence of American consumers.Would buying these stocks now be a hot-weather impulse or a coldly-calculated move?All six have improving earnings outlooks, analysts say. Credit-card companies and UnitedHealth appear to be the best bets.The six companies share similar traits that make them attractive. They are consumer-focused, with dominant market positions and growing revenue streams, says Fred Dickson, chief investment strategist at D.A. Davidson & Co.Their importance to shoppers is crucial to their growth prospects. Americans' confidence in the economy has reached its highest point in 5 1/2 years. The housing recovery is strengthening. Job growth continues at a steady pace.When consumers feel better about the economy, they splurge on discretionary items like a Venti Caramel Macchiato from Starbucks or a new book or DVD from Amazon. And they pay for those items with credit cards.Visa and UnitedHealth are the most attractive buys right now, says David Brown, chief market strategist at Sabrient Systems, an investment research firm.The outlook for Discover and MasterCard is also good, particularly as consumer confidence improves. The companies' biggest challenge remains staying competitive in a crowded field, he says.While Brown expects Amazon to continue to dominate its market, he sees a big risk in buying the stock now."It's a fine company, but I would want to enter it in a pullback - a big pullback," Brown says. "It has, by far, the most downside."Here's a brief summary of each stock:- UnitedHealth Group Inc.The stock of the nation's largest health insurer has climbed more than 25 percent this year and hit an all-time high of $68.75 in trading on Wednesday, according to FactSet.Like other health insurers, UnitedHealth stands to benefit from the federal health care overhaul. The company will be able to participate in state-based health insurance exchanges designed to expand coverage to millions of uninsured Americans. The company is also the largest provider of Medicare Advantage plans, which are privately run versions of the government's Medicare program for the elderly and disabled people.Financial analysts, on average, expect the stock to move higher. Their consensus target price is $71.47, according to FactSet.On average, the stock has a "Buy" rating from analysts polled by FactSet.- Amazon.com Inc.Amazon's stock price is up about 23 percent this year and touched an all-time high of $307.55 in trading on Friday.Sales for the world's biggest online retailer have been growing as Americans' confidence in the economy improves and they shift to online shopping. A key rival, Barnes & Noble Inc., is struggling with weaker sales and big losses driven by its Nook e-reader, a competitor to Amazon's Kindle.Analysts see Amazon shares moving higher still. The average target price on the stock is $316.79.Even so, some investment experts sense a bubble.Brown has a "Sell" rating on the stock, which he believes is overpriced. He points to Amazon's "forward" price-earnings ratio, which compares a stock's price to projected earnings over the next 12 months. Not all agree. Amazon has an average analyst rating of "Overweight," which indicates the average broker rating falls between "Hold" and "Buy."On that basis, Brown says investors buying Amazon's stock now are paying 100 times future earnings.- Starbucks Corp.Starbucks' stock is up 30 percent this year and reached an all-time high of $69.72 in trading on Friday. That's barely above the consensus target price of $69.62, according to FactSet.The coffee chain, with more than 18,000 stores around the world, has delivered strong growth in the Americas and Asia, where it has opened more shops. Last year it introduced a single-serve coffee machine and branched out beyond coffee by acquiring tea shops and bakery chains, and a bottled juice company.But it faces increased competition from fast-food chains such as McDonald's, which have expanded their coffee offerings. On average, the analyst rating on the stock falls between "Buy" and "Hold."- MasterCard Inc.The stock is up 22 percent this year and reached an all-time high of $602.74 in trading on Monday.The credit and debit card company, which makes money from processing charge card transactions, thrives when consumers are in a spending mood.MasterCard has been focusing on developing countries, where most transactions are still done in cash. As shoppers there shift from paper money to plastic, MasterCard can tap into that growth.A consensus price target of $614.61 suggests that financial analysts see further growth ahead for the stock. But those surveyed by FactSet are split between "Buy" and "Hold."- Visa Inc.Visa's stock is up about 26 percent this year and reached an all-time high of $192.77 in trading on Monday. Visa remains the industry heavyweight. It has also taken steps to make its payment-processing business more accessible to mobile-device users."Visa has done an amazing job, really, of capturing revenue and new cardholders and turning it into earnings," says Brown.Analysts see the stock advancing. Its consensus target price is $197.12. Analysts polled by FactSet are divided between recommending a "Buy" and a "Hold."- Discover Financial ServicesDiscover's stock is up 32 percent this year. It rose to an all-time high of $50.92 in trading on Friday - below the consensus target price of $52.73.Beyond its namesake credit card, Discover has moved into auto, personal and student loans, as well as home equity loans.The Fed's signal last month that it could begin tapering its bond-buying program, which has helped keep interest rates low, is potentially good news for Discover and other credit card issuers. As interest rates rise, they typically translate into more revenue for card issuers. That's something investors are anticipating, says Dickson.On average, the stock has a "Buy" rating from analysts polled by FactSet.