What ever you get try get breathable or I used to use and old bed quilted sheet under soak up moisture then let it dry out during day.
Also be careful of bike being blown over if out in open.
After about a year the UV got to it and it all just started to get very brittle and started to fall apart at the seems, so went and bought the more expensive one as the shop ensured me it was of much better quality:
At first it did seem like a much better well made product but again after about a year it faded a lot, went brittle and just fell apart.
Bear in mind that the bike was stored in a lock up over the winter and I only used the cover during the summer months (we get rain in the summer).
At the time I had no choice but to park my bike in direct sunlight the whole day so the only advice I can give is to try to park it in the shade, I'm certain that the above covers would have lasted a lot longer if I'd been able to do that. FYI the more expensive one was much better made and was 100% waterproof. They also claimed it was UV resistant but I found that to no be the case at all, UV is extremely harsh on materials like that.
Also when looking at different sizes, make sure you factor in the height of your mirrors, as obviously they are the tallest part of the bike so therefore determine the overall height of the cover that's needed.