Apple's (NASDAQ:AAPL) upcoming phablet, the iPhone 6 Plus, will face significant competition this fall: The fourth iteration of Samsung's (NASDAQOTH:SSNLF) category-defining Galaxy Note will debut just weeks after the iPhone 6 Plus goes on sale.

Compared to standard handsets, both phones are enormous, with their gigantic screens blurring the line between traditional smartphones and tablets. Still, when it comes to physical dimensions, there's a major difference: Although Apple's iPhone 6 Plus has a smaller screen than Samsung's Galaxy Note 4, courtesy of Apple Pay, the device itself is much longer and nearly as wide.

iPhone 6 Plus vs. Galaxy Note 4
The iPhone 6 Plus is 158.1 mm long, 77.8 mm wide, and 7.1 mm thick. The Galaxy Note 4 is only 153.5 mm long, just slightly wider (78.6 mm), and a bit thicker (8.5 mm). That extra width and thickness, however, bring much more screen real estate -- in contrast to Apple's 5.5-inch 1080p screen, Samsung is offering a quad HD display that measures 5.7 inches diagonally.

Size matters
A few tenths of an inch and a half-dozen millimeters might not seem significant, but these phones are defined entirely by their size. Although both handsets offer slight perks over their smaller counterparts (notably superior battery life), the big selling point is clearly that enormous screen.

With the iPhone 6 and iPhone 6 Plus debuting on the same day, many articles have attempted to answer the obvious question: which is the superior choice? Almost invariably it comes down to trade-offs, with would-be buyers having to decide if that extra screen space is worth lugging around a gigantic phone.

From that perspective, Samsung offers the better deal: the Galaxy Note 4 gives buyers far more screen for not much more phone.

Apple needs that big bezel
Of course, it's not particularly surprising that Apple's phablet is longer than Samsung's. The iPhone's iconic, circular home button requires an equivalently big bezel, and by extension, a longer phone. Samsung's Galaxy Note 4, meanwhile, has a much smaller, lower bezel. Samsung's phone also has physical home button, but it's not as large as Apple's, and is shaped differently.

It's hard to imagine Apple's design changing, at least not in the near future, because of the increasing importance of that home button -- it contains Touch ID, which is directly tied to Apple Pay, the company's big bet on the future of digital payments.

Samsung's Galaxy Note 4 also includes a fingerprint scanner, but like the Galaxy S5, it works much differently than Apple's feature. Rather than users simply hold their thumb on the button (as per Apple's Touch ID), Samsung's solution requires them to slowly drag their finger across the lower portion of the screen. Apple's Touch ID is not without its critics, but Samsung's fingerprint scanner has been almost universally derided, with reviewers in the past remarking that it works, at best, half the time. It's possible that Samsung has improved it significantly with the Galaxy Note 4, but the very concept seems less ideal than Apple's.

Can the iPhone 6 Plus convert Android fans?
Apple appears to be betting that Apple Pay will emerge as a must-have feature that could set its iPhones apart. That could certainly be the case, but it's not without trade-offs: namely, bigger bezels and less real estate for the screen.

Samsung's Galaxy Note 4 isn't the only phablet that the iPhone 6 Plus will have to compete with. The LG G3, which debuted earlier this year, sports an identically sized 5.5-inch screen, but the device is almost half an inch shorter and more than 3 mm narrower than the iPhone 6 Plus. 

Apple is clearly looking to lure fans of these Android phablets over to its device (it has even created a how-to website detailing the most painless way to make the switch). Many, perhaps enticed (at least partially) by Apple Pay, could take the leap, though I expect some will be turned off by a phone that simply offers less screen for its size.

Sam Mattera has no position in any stocks mentioned. The Motley Fool recommends Apple. The Motley Fool owns shares of Apple. 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.