With energy prices constantly fluctuating, it can be hard to decide the best place for your investment dollars in the energy world. We asked some of our Motley Fool analysts to weigh in with their opinions about which energy stock they like right now. In Part 1, we focus on oil and gas stocks; in Part 2, on consumable fuels and infrastructure, and in Part 3, on alternative energy. Read on to see our Fools' ideas.

David Lee Smith, Fool contributor
The world of energy has changed more dramatically during the past five years than in any decade since its inception. And since that rate of change is certain to accelerate further, I've become a stronger fan of oilfield services kingpin Schlumberger (NYSE: SLB).

The industry's primary changes have involved new technologies for coping with the increasingly challenging venues to which companies are venturing. For instance, producing gas and oil from unconventional sources has arrived at warp speed, as have deepwater operations, and dealing efficiently with tar sands and other heavy oil.

This isn't to say that Halliburton (NYSE: HAL), for instance, hasn't contributed real technological advancements of its own. But with 25 research and development facilities worldwide, and more than $900 million devoted annually to its research efforts, Schlumberger is formidable in leading the way technologically.

Change can also refer to geopolitical upheavals. For instance, the Russian market is opening up rapidly to the oilfield services companies. But with the Russian authorities' history of leaning on western companies, it's logical that the sizable Schlumberger is especially well equipped to hold its own when faced by contentious circumstances.

Click here to add Schlumberger to your watchlist.

Michael Olsen, CFA, Motley Fool Special Ops senior analyst
Natural gas is controversial. With the discovery of purportedly vast shale gas stores, the rhetoric among pundits is unanimous: This time, it's different. The arguments differ, but they tend to fall into one of three categories:

1. Natural gas prices will never recover. The newfound abundance of low-cost stores will depress prices eternally, forever languishing at $4/mcf (thousand cubic feet).

2. The sheer magnitude of domestic stores -- estimated at some 1 trillion cubic feet -- will forever transform our nation's energy infrastructure.

3. This isn't your father's natural gas: Shales actually don't make money. It's a Ponzi scheme, according to The New York Times.

I'd argue it's at once different, and not. Whatever your stripe, I think Ultra Petroleum (NYSE: UPL) -- owner of some of the industry's best, and lowest-cost, assets in Wyoming's Pinedale Anticline and the Marcellus Shale -- is the way to play this poker match.

First, a brief discourse on how it's not. Laws of economics haven't been suspended. For a prolonged period, producers have brought gas to market at uneconomically low prices. That's not sustainable, and I'd argue that soon enough, natural gas prices are poised for a recovery.

And yes, by many accounts, there's a lot of natural gas. Amid an increasingly carbon-conscious, politicized energy debate, that bodes well for the commodity's prospects. As for shale gas's profitability (or lack thereof), I'd ask a simple question: Would an entire industry -- and the very economically minded ExxonMobil (NYSE: XOM), via its acquisition of XTO Energy -- continuously risk its well-being on a known uneconomic quantity? I'm well-versed in the sundries of tulipmania, and I'd still wager no.

Now, back to Ultra. The company's industry-leading cost structure positions it to reap a windfall in an eventual price recovery, and its vast undeveloped acreage provide potential for above-market growth for years to come. Better yet: Even if prices don't recover, I'd wager the shares are still cheap.

Click here to add Ultra Petroleum to your watchlist.

Chuck Saletta, Motley Fool contributor
Natural gas will clearly play a critical part in the future of energy. Environmentally, it's cleaner than either coal or oil. Economically, these days, it's also cheaper than both, too. And from a usability perspective, natural gas is flexible enough to provide fuel for the trifecta of heat, electricity, and transportation.

With that in mind, what better energy stock can there be than a large player in processing, transporting, storing, and distributing natural gas, like Spectra Energy (NYSE: SE)? Spectra was spun off from utility giant Duke Energy (NYSE: DUK), but it's now a Fortune 500 company in its own right.

Trading with a price-to-earnings ratio in the mid teens, Spectra is not outrageously expensive, even before we consider any future energy shifts toward natural gas. And with a 3.8% dividend yield, you get paid well above overall stock market yields to wait for that future to arrive.

Spectra Energy is decently priced for the present, smartly positioned for the future, and pays you well to wait for that future to arrive. When it comes to energy stocks, what's not to love about Spectra?

Click here to add Spectra Energy to your watchlist.

Click here for Part 2 of this roundtable or check out The Motley Fool's free report, "The Only Energy Stock You'll Ever Need."

Fool contributor Dan Dzombak holds no position in any company mentioned. Fool contributor Chuck Saletta did not directly own shares of any company mentioned in this article, but his wife owned shares of both Spectra Energy and Duke Energy. Mike Olsen owned shares of both Ultra Petroleum and ExxonMobil. The Motley Fool owns shares of Ultra Petroleum and Schlumberger. Motley Fool newsletter services have recommended buying shares of Spectra Energy. 

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