I seem to remember this subject has come up every so often so I thought I'd post my thoughts on the matter and talk about what I found.
Historically I've been using the properly fitted SeaRay Winter cover, which has been with the boat for years. Unfortunately it's old technology, but it's very breathable and can be watertight when treated. However its getting old now and has been patched in places so I've had a tarpaulin slung it over for the last two years whilst it's been outside (previously kept in a barn). The bespoke covers are very expensive but I suppose if I was to take into account how long this one has lasted not too bad and if you are considering keeping a boat for a few years probably worth the investment.
Tarps are great for airflow but look untidy and are a pain to tie down properly. They are also UV hungry and with the fine weather this summer it disintegrated over the bow section.
A new Tarp would cost about £50-70 depending who you buy it from and what weight the weave is, so I looked around at alternatives. I found a number of different shaped covers at Amazon, Ebay, Marinescene, Force Four etc all looking the same but with different prices and claiming to be extra tough, these ranged from about £30-50. I remembered someone on here bought a cheap cover and it fell apart quickly, so I read the reviews and sure enough loads said stay away.
I took a stroll around the boat park and several boats had covers which had been on for a few years and looked in good order, so I took a sneak peak and they were made by a company called Ducksback, I read the reviews and didn't find a bad one, so I bought one. I don't particularly like the bright Silver colour and they don't fit as well as a fitted cover but its fairly close. They looked as if they were made from very thick pvc or some sort of heavy plastic but when I opened the box it is like a tight weave and has a liner too. It comes with a bag and tie straps.
The tie straps don't get thrown over the boat and wrap around it, but instead the cover has 3 straps sewn into it which then attach to straps that go underneath the boat.
It has 3 attachments at the stern for tying down …
So here it is, not as neat as some but for the price not too bad.
And here is the old one...
We can only wait and see, if it rips apart in the first year, then it goes back.