Tablets are hot. Laptops are versatile. eReaders are inexpensive. So which is the best fit for your back to school bag?

At the end of the day you may well go with the gear that sings to your heart. Let’s face it, a lot of times the final factor in buying a gadget comes down to a gut feeling loosely translated as, “Yeah, I know this one makes the most sense, but that one’s SO FREAKIN’ COOL!” But before you head for the register in a fog of blind lust, at least do a little homework so your head gets a say in the matter along with your heart.

Start by assessing what you actually need, what you can afford to spend, and what will best fit into your current ecosystem.

Needs: What will you actually use this thing for? A lot of that depends on your ecosystem, but first start with the basics: Do you want a full-fledged portable computer with Web browsing, Email, Audio/Video and a hard keyboard? Do you only need something Kindle-sized to take the place of lugging around a dozen print textbooks? Or are you looking for something in between, a reading/browsing machine that can pull double duty as a quasi-laptop in a pinch? To me, a “Yes” to #1 Above means laptop, #2 means eReader, and #3 spells tablet.

Beyond that, what do you know about your school’s requirements and tech environment? Will you need to run special software or connect special peripherals in your field of study? No point getting a tablet computer if you need, say, CAD/CAM software for your design classes that only runs on laptop-class machines. Adriana also reminded me that iPad users sometimes run into trouble connecting to unfamiliar Wi-Fi networks – what does your school support/recommend or even flat-out not allow when it comes to devices running on their infrastructure? If you can, contact your school’s IT department and find out all you can before you buy.

Budget: If you’ve got unlimited cash and want to spend it, you could always just buy one or two from each category and maybe setup a dorm room lending library. But for the rest of us, budget is a factor. An ultralight laptop is most likely your most versatile solution, but even the cheapest ultralights cost about double what a tablet will run. For $400 or so you can pick up a dual-core Android 3.x tablet, HP TouchPad, or last gen iPad. Add a hundred bucks and you’ve got yourself a base model iPad 2, which is arguably a better value than the older, cheaper model. Tablets are a great value if they truly fit your needs, but $400+ is a lot of cash to throw at something if you won’t wind up using it – definitely consider the utility of a mid-range laptop before giving into the cool factor of a Galaxy Tab.

eReaders are more of a speciality item. If your school supports electronic textbooks and you can save cash, paper, and the hassel of carrying heavy books by going with an eReader instead, go for it! Just be sure to check out the device’s note-taking capabilities before you buy – highlighting and annotating on an eReader isn’t going to be the same as doing it by hand in a print textbook.

Ecosystem: In all likelihood this will be the determining factor in the Tablet/Laptop/eReader battle. What tech do you already have, and how do you use it? If you’re starting from scratch, go with the laptop. It’s the best bang for the buck and can serve as everything from portable note-taking device to dorm room home theater. Have a serviceable desktop computer already and want something to take to class and the library? That’s different – a tablet is easily stashed in a backpack, can get you through most situations in a pinch, and offers all-day battery life. You can always head back to your room when you need the heavy lifting power of your desktop machine. Already have a laptop and headed to a school that supports eBooks? A Kindle or Nook won’t take up much space in your bag (or pocket), and makes a pretty nifty conversation starter at the campus cafe, to boot.

Then there’s the smartphone/camera/iPod factor. What other gadgets can’t you live without? Are you tied into the iPhone/iTunes/Apple TV ecosystem already? Or maybe you’re a card-carrying member of the Android Army? Brand loyalty has taken on a whole new meaning in today’s world of digital media and proprietary standards. Sometimes you have to compromise to find true happiness, you know? So think about things like, “How do I listen to music? What devices are compatible with my music collection? What’s the easiest way to sync those devices up?” and you might wind up realizing that an Android tablet just won’t play nicely with your Windows Phone 7 smartphone, or as cool as the HP TouchPad is, you really need a laptop to manage your photo collection.

Buying Recommendation: When in doubt, buy a laptop first. As much as I’ve fallen for Nook and as cool as tablets are, there’s still no doubt in my mind that for the majority of back-to-schoolers out there, the laptop wins this battle hands-down. Like I said, if you’ve got the budget for it, you can certainly make the case for adding a tablet and/or eReader to live alongside that laptop in your high-tech campus lifestyle. And those of you who are already arguing in your heads why a tablet would be perfect for your needs, you’re probably the exceptions to the rule, so enjoy the “Post-PC” world.

But for the rest of you headed off to campus in the fall, I say put your graduation money towards a light but durable laptop with a crisp screen and good battery life. Then make friends with a kid down the hall and borrow his tablet whenever you get the itch. You’ll be set, computing-wise, and have a new pal to boot!