I use the standard blue 8mil cover which I have found to last about the same as the 12mil covers. I usually get 2 years out of the 8mil and I got 2 1/2 years out of the 12mil so I decided the price difference wasn't worth it.

For me I end up getting about an extra month on both ends of the season with using one. I leave the cover on all the time except when swimming of course, and then I leave it off once the temps start to stay in the mid to upper 80's for the day.

Maybe the diamond design or different colors work a little better but I haven't seen anything that convices me that it is worth the extra cost.

My suggestion is to start out with an 8 or 12mil cover and see how it works for you and in a couple of years you will have the opportunity to replace it with something else.