We've run down the differences between Ethernet cables. Each newer standard brings higher possible speeds and reduced crosstalk, which helps you achieve those speeds even with longer cables. The above table highlights the specifications of each category.
The reality is that a Cat-5e cable with it's up to 1 Gb/s speed is fast enough for your Internet connection. That 1 GB/s speed supports anything up to a Gigabit Internet service, so you won't see any increase in your Internet speed if you switch from Cat-5e to a higher category cable.
However, if you do a lot of transferring data between computers on your local network, upgrading may be worth it. And, if you're buying new cables or wiring your home right now, you should at least use Cat-6 instead of Cat-5e cables. If the price difference isn't too much when you wire your home, you might even go for Cat-7 cables. Just be aware that working with Cat-7 cabling requires a little more finesse that working with Cat-5e or Cat-6 cables—mainly because it’s easier to damage the foil shielding when bending Cat-7 cables.
Category 5 (Cat-5) and Category 5 Enhanced (Cat-5e) are actually basically the same. Nothing changed physically in the cable itself. Instead, Cat-5e cables are tested more stringently to ensure less crosstalk (electrical interference). In other words, only some of those old Cat-5 cables are good enough to be Cat-5e cables.
Cat-6 and Cat-6a cables are more interesting. If you have a modern router and modern Ethernet-enabled devices, you can get faster speeds—10 Gb/s for Cat-6a instead of the 1 Gb/s for Cat-6. The rest of your hardware has to support it, too, but you won't get those above 1 Gb/s speeds unless you have good enough cables. If you plug all your great new network hardware into old Cat-5e Ethernet cables that you ran through your home's walls years ago, you won't get the full speeds.
Cat-7 cables really don't offer too much advantage over Cat-6a, at least not for the home user. They use a little better shielding, which can help maintain better speeds at longer distances, but it's nothing remarkable. If the price difference is small, and you're having someone wire your home, consider going with Cat-7 just for some extra future-proofing. Otherwise, Cat-6a should be just fine for new installations.
This doesn't mean you should rip your home's walls open to replace Cat-5e cable installed years ago, especially if you don't have a need for faster local network speeds. But not all Ethernet cables are equal.