The quick-serve restaurant space has been serving up an interesting -- and choppy -- earnings season. Hot or cold? Starbucks (NASDAQ:SBUX) is currently among the hot, having reported quarterly results that investors loved last night.

Hot, hot, hot
Starbucks' third-quarter operating income increased 25% to $615.2 million, or $0.55 per share. Total sales jumped 13% to $3.7 billion. Global comparable-store sales increased 8%, with 7% of that made up of all-important traffic growth. Lower costs, for example for coffee, also fed into the cafe giant's improved profitability.

In the company's press release, CEO and founder Howard Schultz described the company's digital, card, loyalty, and mobile initiatives as creating a "flywheel" effect that is increasing momentum for growth and profitability.

Starbucks also mentions initiatives investors can feel strongly about. The current yogurt craze is pretty obvious, and Starbucks isn't missing the boat. Its recent announcement that it's teaming up with Danone to provide Greek yogurt parfaits sounds probiotically positive, for example; those parfaits will be co-branded with the company's juicing unit, Evolution Fresh.

Starbucks isn't backing away from its strange bedfellows, either. It's expanding its partnership with Green Mountain Coffee Roasters, having shipped its one-billionth Starbucks- and Tazo-branded K-Cup in the quarter for the Keurig single-serve beverage machine.

In another forward move into food, Starbucks is further increasing its offering of La Boulange products in stores, now counting 1,076 cafes carrying the baked goods.

Starbucks' success in bringing in the customer traffic echoes that of Chipotle Mexican Grill (NYSE:CMG), which recently re-established itself in investors' good graces with its quarterly results. Chipotle's comps increased 5%, and again, this was mostly due to more customers darkening its doorsteps -- a very bullish sign, among others.

When the bread doesn't rise
When it comes to hot and not, though, one quick-serve concept's stock has had a rough week. Panera Bread (NASDAQ:PNRA) shares took a beating after its quarterly results disappointed investors. Same-store sales increasing 3.8% caused that bread's failure to rise, since analysts had expected a 4.5% bump.

Starbucks is clearly on a roll right now, as is Chipotle. Is it time to buy either of those darlings? At this moment, count to 10 before pulling the trigger. Cautious investors who get nauseated by stock prices' ups and downs might want to wait until traders (and prices) cool down a little bit.

Granted, Starbucks and Chipotle are both super-strong companies, and in my opinion, solid long-term holdings. I own shares of both in my personal portfolio, and have bought shares for the real-money Prosocial Portfolio I manage for Although I wouldn't say buying either one today is a grievous mistake for long-term buy-and-hold investors -- and there are far weaker companies out there that investors are snapping up at overblown prices -- good things come to those who wait in investing, and quarterly euphoria is a fickle thing.

Right at this moment, of the three quick-serve concepts, Panera -- the "cold" one -- is the best buy, in my opinion. Like the other two, it's also a very strong company keyed into consumer trends (and it's also one of the stocks in the Prosocial Portfolio, incidentally).

This week, disappointment has laid Panera shares low, and anyone who felt they missed the boat can dig in now. Consider Chipotle: When near-term bearishness tore it down, investors should have seen opportunity instead of calamity. Those who bought at its 52-week low of $233 are happy campers right now.

Long-term shareholders can rejoice about the strength that Starbucks and Chipotle exhibit. I'm pretty pleased, myself. But when it comes to looking for a cheap stock idea today, Panera's beaten-down price means it shouldn't be dismissed to the back burner.

Alyce Lomax owns shares of Chipotle Mexican Grill and Starbucks. The Motley Fool recommends Chipotle Mexican Grill, Green Mountain Coffee Roasters, Panera Bread, and Starbucks. The Motley Fool owns shares of Chipotle Mexican Grill, Panera Bread, and Starbucks. Try any of our Foolish newsletter services free for 30 days. 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.