Just a random thought for a Saturday afternoon: While I’ve had some pretty strong opinions about what I perceive to be the optimal size and aspect ratios of the screens on smart phones and tablets, this fall’s bumper crop of new devices has me rethinking things. And I don’t mean I’ve arrived at new optimal sizes and aspect ratios. I mean there’s no one answer.

For example, for the past few years it’s been pretty easy to complain that the iPhone’s screen size was too small compared to the ever-increasing screens on competing Android devices … because it was. (My comment that the iPhone 4S was “perfect for women and children” was infamously—and incorrectly—turned on its head to appear misogynistic when in fact it was just about the size of the device.)

Apple responded to this obvious complaint in a wonderfully non-standard way. Instead of creating a bigger screen with the same aspect ratio as its predecessor, it provided the iPhone 5 with a screen that was stretched out only vertically. That is, while the pixel count horizontally remained at 640, Apple increased the vertical pixel count from 960 to 1136.

Apple’s decision to increase the size of the iPhone 5 screen only in the vertical was explained by Apple vice president Phil Schiller during the iPhone 5 launch event. So while the firm moved from a 3.5-inch screen to a 4-inch screen, it obtained a natural 16:9 aspect ratio that it conspicuously does not use on its other mobile products, including the more recently released iPad mini. Why?

“It is really easier to make a new product that is bigger, everyone does that,” Schiller said, noting that the ‘design center’ for a phone is your thumb. “A phone should be easy to use with … a thumb. It should be easy to send messages, type emails, surf the web, and that’s how we designed iPhone 5.”

In other words, had Apple simply moved to a larger 4-inch screen and increased the size of the screen in both the horizontal and vertical, as other phone makers have done, many users wouldn’t be able to use the device with one hand.

Now, as a bigger guy with big hands, I don’t mind the bigger phones, but I can see the point. And certainly many people aren’t too interested in a Lumia 920 or the even huger Samsung Galaxy Note because of the screen sizes. But conversely, others are attracted to these devices for exactly this reason. One size doesn’t fit all.

On the tablet front, I’ve long argued that a 7-inch device makes a lot more sense than a 10-inch device when that device is primarily a content consumption device and not a creation device, like a tablet PC or hybrid laptop. I made this argument when the first iPad came out and, since then, I’ve really enjoyed smaller devices like the Kindle Fire, Kindle Fire HD, and Google Nexus 7.

But screen size wasn’t the only physical difference between the iPad (pre-mini) and these other devices: The competing 7-inch tablets all offered widescreen aspect ratios and not the boxy 4:3 aspect ratio Apple’s used on the iPad. I was curious whether Apple would go the iPhone 5 route with the iPad mini (using a 16:9 aspect ratio) or whether it would retain the classic 4:3 screen type of its predecessors.

As you probably know, it chose the latter route. And its explanation of this decision, which is initially a bit odd given that the iPad mini, like the iPhone 5, is designed for one-handed use, goes as follows. Apple wanted the new iPad to be a no-brainer for developers so that all existing iPad apps would just run. (On the iPhone 5, existing apps all run too, but they leave black bars on the sides of the wider new screen. And don’t get all hatey on me, this is exactly how Windows Phone 8 does it on HD displays too.) “The iPad mini is the most usable of all these [small tablet] devices,” Mr. Schiller explained a month later at the iPad mini launch event. “All of the software created for iPad works on iPad mini … unchanged.”

What’s interesting about these two devices is how different they are from the rest of the market. Other smart phone makers tend to produce much bigger screens, period, screens that are bigger in both directions than the iPhone 5. (Certainly, no company makes a tall, thin screen like that on Apple’s device.) And tablet makers have generally eschewed the 4:3 aspect ratio of the iPad/iPad mini and have gone with widescreen designs.

I’m not sure which I like better.

My current smart phone, the HTC Windows Phone 8X has a 16:9 widescreen (1280 x 720) display. This screen is 4.3 inches, so it’s a bit bigger than the iPhone 5 screen. And while I love this device, I have the same issue typing on its virtual keyboard that I do on all iPhones: They keys are a bit small (probably tall and thin really) compared to the phones I previously used. So I find myself making more typing mistakes than I had previously.

The thing is, the virtual keyboard on this device isn’t that much smaller than it was on the Focus S or Lumia 900. But it is smaller. (The iPhone keyboard hasn’t changed. It’s just small.)

Meanwhile, I’ve been using a Kindle Fire HD since it came out and really enjoy the device, though as I noted in my review, the bezels around the screen—which is tall and wide—are oddly huge. The Fire HD is great for reading books and for watching video content, and I’d never really considered any particular shortcomings in the device.

Until I got an iPad mini. This device has a wider screen, and much smaller bezels, and is lighter and thinner. Yes, video content is letterboxed. But who notices that? Web content looks great, and the reading experience is great too. The screen, though lower-resolution, looks great to me. (I suspect a future retina version of the mini will change my mind. I can wait.)

These new devices have thrown my worldviews out of whack.

I really can’t decide between 16:9 and 4:3 smart phones and tablets anymore. Each has its pros and cons. And while the devices you choose won’t typically hinge on this particular spec, maybe that’s the point: It shouldn’t.

One final bit of confusion. Sitting in the press room at BUILD, I ran into PC World’s Melissa Perenson, who was carrying a genre-busting Samsung Galaxy Note II. This device is somewhat ludicrous on the surface with its 5.5-inch (and 16:9, 1,280 x 720) display. But looking at this beast—which is actually really thin and light as well—it occurred to me that phone calls were not my most frequent activity on a smart phone anyway. And email, calendar, web browsing, and other tasks are much more enjoyable—especially to my aging eyes—on such a device.

Sigh.