Some of the advantages over laptops, to name a few are: tablets have touch interfaces, although, some laptops/ hybrid laptops are becoming equipped with touch interfaces, most of the time, it's a tablet attached to a keyboard, but having a little hand-held device that doesn't need a clumpy keyboard really adds to the portability, of what's already a really portable device. Apps and other fun little gadgets, you might get a lot of functionality with laptops, but with tablets, and tablet-like devices, you're able to download neat little applications to help with school and other tasks during the day. Tablets pack A LOT of power for a small device, since tablets are now being equipped with Core i7's and strong nVidia and AMD hardware, they're becoming increasingly stronger by the month, laptops will ultimately become inferior products.
A desktop PC would be my first choice.
Although it's not as portable and small as a tablet, or a laptop, but they pack more power (literally too) and they usually cost less for the same hardware as a laptop. You can also build small desktops, with M-ITX, or M-ATX motherboards, and small little cards, for example, the Asus Direct-CU Mini GTX 670, and the MSI M-ITX 760, fit them into a small case by CoolerMaster, or Bitfenix, and you're good to go. Although, you still have to carry around a heavy monitor and your peripherals, but desktops are very future proof and tinker-able.
Mobile operating systems are sometimes weird to operate and a little confusing, but they're really all different, in terms of their aspects. iOS, is responsive, but is very non-user friendly, from their poor tech support "Geniuses" and the layout of iOS7 in attempt to look metro and modern. Windows Mobile Operating system is customizable but is very poor in terms of apps and features. Linux Ubuntu OS has a nice sleek design and VERY user-friendly, but isn't well known, and would make people speculate whether to buy one or not. So, there aren't any serious advantage to any one mobile operating system, since they're relatively the same, it's all user preference.
I'm not very good at writing, in fact, I'm absolutely shit at writing essays and papers and what-not. I thought I'd pass some time by writing that, since it's really early in the morning and none of my friends are up right now, so forgive my mistakes if I've made any :)