We use our tub an average of about twice a week. I normally turn the temperature down to about 85 and set it in economy mode until the next time we want to use it.

Can anyone tell me if there is a "best" temperature to set the tub at when not in use?

Remember that on most spas it takes up a lot more power to heat it up then it does to maintain temperature, if you have a cover for the spa it would probably be best to just leave the temp wherever you prefer it and then set it to the economy cycle's, it should at that point maintain a decent temperature and not cause as much of a strain on your electric bill.