It seems logical to try to purchase shares of a stock after it has declined. To be sure, "Buy low, sell high" is an oft-repeated mantra among value-seeking investors.

But keeping in mind there's usually a good reason behind the declines of most stocks, experienced investors know another counterintuitive approach can be even more effective. That is, the idea that winners keep on winning, and that buying stocks at all-time highs can mean watching them continue to march ever higher.

So we asked three top Motley Fool investors to each give us a stock at all-time highs that they believe is still worth buying. Read on to learn why they chose Markel (NYSE:MKL)Cheniere Holdings (NYSEMKT:CQH), and AveXis Inc. (NASDAQ:AVXS).

Man standing on ladder, drawing climbing returns chart on a brick wall

IMAGE SOURCE: GETTY IMAGES.

This mini-Berkshire will keep climbing over the long term

Steve Symington (Markel): It might seem intimidating to buy Markel after it briefly topped $1,000 per share for the first time earlier this week. But this specialty insurance and financial holding company did so with good reason.

First, don't be scared by its "high" share price. Often referred to as a mini-Berkshire Hathaway (NYSE:BRK-A)(NYSE:BRK-B) (note that Berkshire's Class A shares trade around $258,000 apiece as of this writing), Markel not only bears a striking business resemblance to the company Warren Buffett built, but it also doesn't make a habit of instituting the zero-sum game that many investors know as stock splits to make its shares falsely appear more attractively priced. 

Rather, Markel owes its success -- and management's bonus compensation is tied -- largely to its ability for growing its book value per share at outsized rates over long periods of time. As of the end of last quarter, for example, Markel's book value per share had climbed 5.2% year over year to $620.30, leaving shares trading at a reasonable (albeit not terribly cheap) price-to-book ratio of 1.6 as of this writing. To be fair, that's well below the incredible 13% compound annual growth in book value per share that Markel has achieved for the past 20 years. But given the proven ability of its three primary business segments -- insurance operations, a portfolio of diversified non-insurance businesses operating under Markel Ventures, and an investing segment -- to consistently create shareholder value over the long term, I think it's only a matter of time before we see that growth revert to Markel's historic levels. And I have no plans to sell my shares even as they stand near all-time highs.

This LNG-fueled dividend is just about to leave the station

Matt DiLallo (Cheniere Holdings): Cheniere Holdings can take a bit of unpacking to understand. Structured as a C corporation for tax purposes, the company holds a 55.9% stake in MLP Cheniere Energy Partners (NYSEMKT:CQP), which owns the Sabine Pass liquefied natural gas (LNG) export terminal in Louisiana. Because of that relationship, Cheniere Holdings receives cash distributions from Cheniere Energy Partners, which it then pays out to its investors via dividends. While that structure adds a bit more complexity, it also allows investors in Cheniere Holdings to collect dividend income, without having to mess with the tax complications that can arise from owning units of an MLP like Cheniere Energy Partners.

That difference aside, what matters most about this relationship is that Cheniere Energy Partners is in the process of building six liquefaction trains at Sabine Pass, which will enable the company to export a growing volume of natural gas under lucrative long-term contracts. It now has completed construction on three of the units, which are generating revenue. These trains have already fueled a significant increase in the company's earnings, which hit $319 million last quarter, up from a mere $12 million in the year-ago quarter. Those higher profits should allow Cheniere Energy Partners to increase its distribution to investors, which would trigger a dividend increase from Cheniere Holdings. In fact, the company expects to pay out $0.90 to $1.10 per share in dividends this year, up from its current rate of $0.80 per share on an annual basis. Because of that forecast, investors have already started bidding up shares of Cheniere Holdings, which recently touched a new all-time high.

That said, there's still plenty of growth left in the tank since Cheniere Energy Partners has two more LNG liquefaction trains under construction and another one in development. Because of that built-in growth, Cheniere Holdings is still worth buying today even though the stock is at the highest level in its history. 

A high-flying biotech stock with more fuel in the tank

Cory Renauer (AveXis Inc.): This clinical-stage biotech stock has more than doubled over the past year, but there are a few reasons to suspect it could climb much higher in the years to come. The company is developing a treatment for spinal muscular atrophy (SMA), a rare genetic disorder, that could send the stock soaring if the candidate continues to succeed in clinical trials.

Children born with type 1 SMA rarely develop the ability to sit up unassisted, and most remain unable to swallow or speak properly. In fact, 1 in 4 isn't expected to survive past 13.6 months of age without constant mechanical breathing support.

It's early still, but it looks like AveXis has a drug in development that could raise those odds a great deal. AVXS-101 employs a viral vector that essentially infects nerve cells with functional copies of the gene these patients lack, and all 15 patients treated were still breathing unassisted at the 13.6-month mark. In fact, a majority of 12 patients given the dosage proposed for further studies were still breathing unassisted at 30.8 months. Even better, many reached motor-skill milestones rarely achieved by type 1 SMA patients.

If AVXS-101 eventually earns approval, it would compete with Biogen's Spinraza, which became the first FDA-approved SMA treatment late last year. If AVXS-101 can repeat the results seen in the 15-patient study, though, the big biotech's treatment shouldn't put up much of a fight. In trials leading to Spinraza's approval, just 61% of SMA patients survived through 56 weeks without requiring breathing support.

Spinraza is expected to generate about $2.5 billion in sales each year at its peak. With an arguably better efficacy profile, AVXS-101 could do just as well if eventually approved. Although AveXis stock is near an all-time high, its recent $2.3 billion market cap is still low enough that success with AVXS-101 could lead to significant long-term gains.

Cory Renauer has no position in any stocks mentioned. Matt DiLallo owns shares of Berkshire Hathaway (B shares). Steve Symington owns shares of Markel. The Motley Fool owns shares of and recommends Berkshire Hathaway (B shares), Biogen, and Markel. The Motley Fool has a disclosure policy.