What is the biggest drone manufacturer in the world? That's a tough question to answer. Honestly, it depends on what you mean by "biggest" -- and how fuzzy you like your math when evaluating unmanned aerial vehicle (UAV) companies.

According to the most recent report out from the drone industry watchers at DroneII.com, for example, the top three largest UAV manufacturers in the world are China's SZ DJI Technology Co. at No. 1 and Xiaomi at No. 3, with France's Parrot sandwiched in between them.

American companies don't even enter the ranks of the top UAV companies before No. 4 player Hover Inc., followed in short order by No. 5 AeroVironment (NASDAQ:AVAV), 3D Robotics at No. 6, and Boeing (NYSE:BA) subsidiary Insitu at No. 7. Counting No. 9 entrant Ehang, that gives America five of the top 10 slots, which is more than any other country can boast.

A Quantix commercial drone in flight.

AeroVironment's Quantix drone is helping lift it into the top ranks of leading drone companies. Image source: AeroVironment.

What's more, DroneII uses some rather fuzzy metrics when assigning ranks to leading drone companies -- factors such as how often a company's name is used in Google searches for terms such as "drone" and "UAV," how often a company's name appears in blog and media postings, and how many employees at a company have words such as "drone" or "UAS" included in their job titles on LinkedIn.

Like I said, fuzzy math.

How investors rank the leading drone companies

When it comes to investors looking to participate in the nascent drone industry, however, the task of figuring out which companies are the biggest drone manufacturers is a bit simpler. Right off the bat, we can discard top UAV companies such as DJI and Xiaomi, and Hover and 3D Robotics, because they're privately owned. We can't invest in them, and so -- to be blunt -- they're therefore of no interest to us.

So who does that leave? AeroVironment and Boeing, obviously -- the only two companies with a ticker -- move to the top of our list.

Neither Boeing nor AeroVironment is a big player in the market for "recreational" drones, the now-ubiquitous camera-toting quadcopters that have made DJI and Parrot famous. Rather, they focus on making drones for the military. Boeing's Insitu is most famous for its ScanEagle drone, which famously played a part in the Navy's rescue of MV Maersk Alabama's Captain Phillips back in 2009, for example. And AeroVironment is the biggest drone manufacturer for the military, having sold literally tens of thousands of drones for the Pentagon over the past few decades.

In addition to their military customers, Boeing and AeroVironment are also spinning up commercial drone businesses. Boeing has touted ScanEagle's usefulness for monitoring wildfires and helping firefighters, for example. And last year, AeroVironment unveiled a large-scale initiative to market its new Quantix drone to industry, advertising the drone as ideal for such uses as surveying oil pipelines for leaks and monitoring the health of farm crops.

Boeing versus AeroVironment

Which of these two companies makes for the better investment? If you're looking for something close to a pure-play drone investment, AeroVironment is clearly the better choice. Nearly 89% of the revenues AeroVironment makes in a year, it makes from selling drones. In contrast, drones represent just the tiniest sliver of annual revenue for Boeing -- about 1%.  

From a valuation perspective, though, the choice swings the other way. With $5.1 billion in trailing earnings, and $9 billion in positive free cash flow, Boeing is both profitable and generates tons of cash. AeroVironment isn't, and doesn't. Sad to say, while AeroVironment is growing strongly in drones, it doesn't appear to be growing profitably yet. 

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.