As an investor, I'm fairly conventional. I tend to put my money in established companies that have proven they can make a buck, and, I feel, have clear potential to make plenty more.

In spite of their differences, the three stocks at the top of my portfolio broadly fit that description. All have done well on a fundamental and a stock price basis since I acquired them. I also still think they have gas in the tank. Here's a brief look at the trio.

Three silver trophies declining in size from left to right.

Image source: Getty Images.

Facebook

Is there anyone in the world who isn't on Facebook (NASDAQ:FB) these days?

Yes, the privacy concerns are valid, and the company apparently did business with The Wrong People in the run-up to our presidential election. But users have learned to accept and cope with the former, and don't seem to be deserting because of the latter. Facebook is far and away the go-to social media platform of our age, and it's not hyperbole to say it's the most impactful and influential site since the dawn of the Web.

It's also a heck of a money maker. The company never seems to stop growing, and its margins are as lofty as CEO Mark Zuckerberg's ambitions.

However, I do believe that historically hot growth will cool. I see signs of it already in the company's recent(ish) pushes -- most of my contacts rarely use the aggressively marketed live video feature, and I've yet to see anyone post an ad in the marketplace section of the site.

Yet, I'm not worried. Facebook is the online connective tissue of our time, and as such is an unavoidable stop for advertisers hoping to hock their wares. The company's business model is obviously effective and sustainable, unlike a great many internet operators with whiz-bang ideas over the years. This has been a great stock to own, and I look forward to holding it in my portfolio.

Western Digital

I inherited shares of Western Digital (NASDAQ:WDC)last year when it closed the cash-and-stock acquisition of top flash memory maker SanDisk.

I didn't expect the company to perform all that well. Even with SanDisk, its core product was the soon-to-be-obsolete traditional hard drive.

But numerous analyses have shown, and Western Digital's performance in the segment strongly indicates, that businesses, in particular, are reluctant to ditch those drives for solid-state models. If anything, they augment them with flash rather than replace them.

At the same time, shipments of flash memory -- the only way to go in smartphones and tablets -- are growing notably. So with SanDisk, Western Digital has a grip on the future of storage, while keeping a hand firmly in the present.

SanDisk is really helping the company's fundamentals. In the fiscal year 2017, Western Digital's revenue zoomed almost 50% higher to $19.1 billion, while adjusted net profit nearly doubled to $2.7 billion ($9.19 per share).

In spite of its heartbreaking loss in the fight for the half of an Asian manufacturing joint venture it operated with Toshiba, analysts are still projecting robust profitability growth in the near future -- fiscal year 2018 per-share net profit is expected to grow by 36%, landing at $12.50.

We're living in a world that's increasingly dependent on flash storage, while the technology's hard drive predecessor is holding on better than expected. Both developments hint at continued growth for Western Digital.

TD Ameritrade

The stock of online brokerage TD Ameritrade (NASDAQ:AMTD) was hit hard earlier this year after rival Charles Schwab (NYSE:SCHW) lowered its standard share trading fee from $6.95 to $4.95. This led to price cuts throughout the brokerage sector. TD Ameritrade refused to race all the way to that $4.95 bottom but did slice its fee from $9.99 to $6.95.

Naturally, this has dinged its commission and transaction fee revenue -- the traditional bread-and-butter for brokerages. The line item dropped by 3.5% on a year-over-year basis in Q3. Meanwhile, TD Ameritrade more than made up for this with good, old-fashioned hustle, notching a fresh record for net new client assets.

Speaking of records, the quarter's net revenue hit an all-time high, rising 11% to $931 million. And the company did a fine job taking in insured deposit account fees while boosting net interest revenue (both up 22%) and collecting more fees for investment products (up 17%).

In short, TD Ameritrade is successfully strengthening its other revenue streams to reduce dependency on commission and transaction fees. In this latest quarter, these made up 58% of overall revenue, well down from Q3 2016's 73%.

The company is bulking up with the just-closed acquisition of peer Scottrade. Looming Fed interest rate hikes should also boost its fundamentals. I'd characterize TD Ameritrade as a best in class stock in the (admittedly small) brokerage segment, and a keeper given its potential.

Eric Volkman owns shares of Facebook, TD Ameritrade, and Western Digital. The Motley Fool owns shares of and recommends Facebook. The Motley Fool has a disclosure policy.