I’m frequently asked this question, and generally there are a few easy questions to ask that will get you an easy answer. Tablets are great little devices for games, reading, movies, apps, etc. Laptops are great for writing papers, editing videos, editing pictures, playing games, watching movies, etc
So which one should you buy? That depends on what you want to do, and how much you have to spend.
Do you want to create something for others to watch or to read? a tablet doesn’t have a keyboard, and the external keyboards you can buy are usually too small to be useful in writing anything longer than a paragraph or two. A laptop is much more useful in this scenario, or even better, a desktop with a full sized keyboard, and a bigger screen. The lack of a big screen, precise controls such as a keyboard and mouse, and power also makes a tablet less useful for making and editing videos and pictures. While there are video and picture editing apps for tablets, they don’t even come close to the power offered by programs for the mac and PC, and the input method of a touchscreen is not accurate enough.
Do you need really long battery life? Tablets generally have much longer battery life than a laptop, because their less powerful hardware takes less battery power to run. Some tablets can run 8+ hours on battery alone, while 3 hours on battery is really good for a laptop.
Do you need to store a lot of pictures and/or videos? Tablets generally don’t come with much storage, so if you want to keep a lot of pictures and/or videos, a laptop is the way to go, and make sure you get one with a big hard drive.
Do you need to show a presentation on a projector or tv screen? While there are some technologies to allow you to do this using a tablet. The only way to ensure compatibility is to use a laptop, and have any adapters you need to go between hdmi, DVI, and VGA.
Generally neither a laptop or a tablet is very good at taking videos and pictures. The built in cameras might be acceptable, but they are rarely as good as those found in even point and shoot cameras or cell phones.
Most of the time it comes down to content creation, or content consumption. If you want to create something, use a laptop or desktop, but if you all you want to do is consume media, then a tablet will work better than a laptop or desktop.