Billionaire David Einhorn of Greenlight Capital believes we are in the middle of the second tech bubble in 15 years. Those who have invested long enough recall how devastating the last time a tech bubble collapsed. He notes that the huge first-day pops of IPOs such as Twitter is indicative of the tech stocks of the late 1990s. Einhorn believes that we should be valuing tech stocks based on P/E ratios, rather than P/S ratios, addressable market, or pageviews.

Hedge fund investor Jeff Ubben of ValueAct has a similar sentiment. But he also feels that certain big-tech stocks are worth owning. His fund owns Microsoft (NASDAQ:MSFT), eBay (NASDAQ:EBAY) and Adobe (NASDAQ:ADBE). All of these big-tech stocks have positive earnings, which is something that should always be considered when searching for worthy investments. 

Things have been changing at Microsoft for the better
The challenging PC-related sales kept Microsoft trading in a tight range for a number of years. It looks to be finally breaking out of this range. Microsoft's earnings beat consensus last quarter. Its earnings came in at $0.68 a share, above consensus of $0.63. And shares of Microsoft are up over 10% for the last three months, while the NASDAQ index is flat.

ValueAct helped push former CEO Steve Ballmer out. The tech company's new CEO, Satya Nadella, believes we are in a mobile-first, cloud-first world. And with this, he is looking to position Microsoft's products on mobile devices and in the cloud. The first major step by Nadella was to open Office to iOS. It also remains to be seen what Microsoft will do with Nokia. In any case, Microsoft still offers investors a solid 2.8% dividend yield. And it trades at a P/E ratio of 15, which is below the industry average and its 10-year average, which comes in at 17 and 19, respectively. 

Adobe's shift to a recurring revenue generator
Adobe has been shifting its business model from perpetual licenses to subscription services since 2011. As you'd expect this makes Adobe's revenues a bit more predictable. Its initial goal when it underwent the transition was to have 40% of revenues recurring by the end of fiscal 2014. It's already blew through those numbers. At the end of fiscal 2013, over 44% of revenues were recurring. 

The problem with Adobe is that it trades at a relatively high P/E ratio. Its P/E is 30 based on next year's earnings estimates. And taking into account analysts' expected earnings growth, Adobe has a P/E to growth (PEG) ratio of 4.5, which is fairly high.

Although the move toward a subscription model is a positive for the company, it still has to get people to sign up for its services in the first place. The company only added 405,000 paid Creative Cloud subscribers during fiscal first quarter, compared to the 402,000 it added in fiscal fourth quarter. Its goal of 3 million paid subscribers by the end of fiscal 2014 remains ambitious, where its current subscriber base is at 1.84 million.

eBay's fight for mobile payments
eBay was fighting with billionaire Carl Icahn against the idea of spinning off its PayPal division. Icahn eventually backed down, but eBay might have a larger problem. Its second quarter guidance came in below expectations when the company posted first quarter results last month.

Its second quarter guidance for earnings per share was $0.67 to $0.69, which was short of the $0.70 that Wall Street was expecting. But the tech company did beat first quarter earnings expectations, which was helped by a robust share repurchasing spree that totaled $1.8 billion in the first quarter.

On the positive side, eBay is repatriating $9 billion in foreign profits.The company might be looking to make an acquisition with the $6 billion that it will have after paying taxes. On the other hand, it could up its buyback program, which is typically a positive sign to investors as it increases a company's EPS.

Over the last year, shares of eBay are basically flat, compared to the NASDAQ index that's up over 25%. The recent pullback in shares, where it was down over 5% on fiscal first quarter earnings, might present a buying opportunity. The stock is now trading with at a P/E ratio of 15 and its P/E to growth ratio is 1.3. 

Bottom line
Whether we're in a tech bubble remains to be seen, but there could see be money to be made in big-tech stocks. While many of the high-growth momentum names don't have positive earnings, the likes of Microsoft, Adobe, and eBay have been generating earnings for a number of years. For investors looking to gain exposure to the sector, but want to avoid the volatile tech stocks, they should have a closer look at Microsoft or eBay, but wait for a pullback in Adobe.

Marshall Hargrave has no position in any stocks mentioned. The Motley Fool recommends Adobe Systems, eBay, and Twitter. The Motley Fool owns shares of eBay and Microsoft. 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.