Breathability is important when you're buying a car cover because moisture trapped under a cover can damage the paintwork. But you generally want something that's easy to use, fits well and has enough tethering to secure the cover in high winds. It comes down to whether you want something cheap that does the job or a cover that offers a bit more quality. I'd recommend the Halfords all-seasons car cover, but it pricier than a lot of the alternatives you'll see on Amazon. The Oxgord car cover is also well-rated.

Aside from the actual cover, there are some things to bear in mind about covering a car. Don't put a cover on a wet or dirty car, it needs to breathe. Likewise, don't keep the cover on for days at a time. If the cover becomes saturated with water, then stays on the car, the water can get into the paint. Then when it gets warmer, blisters can appear in the paintwork. Also, try to find a loose fitting car cover, tight fitting covers don't let the air circulate - which (again) is essential.