There are a variety of different guy line tensioners available, from those simple tensioners that come with a purchased tent to fancy (and pricey) aftermarket tensioners.
Half of the challenge is knowing how to correctly use a tensioner for tightly tying out your guy lines. And we recommend practicing your skills at home so that when you are at camp pitching your tent, you can guy line like a pro.
Here are a few examples of guy line tensioners. The black tensioner on the left is the "Nite Ize Figure 9". The yellow tensioner on the right is a typical unit that is included with the purchase of a variety of tents.
The traditional three-hole tensioner also seems to hold tightest during heavy winds, compared to other aftermarket options that might allow your guy line to slip loose.
Overall, we like the simplicity of the traditional three-hole guy line tensioner that comes with most tents. They are easy to use, they are not an extra expense, and are effective at keeping your guy lines tight.