F,
My vote would be a hot tub.. A hot tub is hot all the time, you just go out and get in it.. It takes a long time to heat up a pool and then you also have to keep it covered. To do it with electricity would be way expensive.
I have a small 200 gallon hot tub, but it is perfect for the wife and me. We use it year round, but more in the winter and a little less in the summer. I'm not sure what it costs to run, but I never even notice an increase in our electric bill after it was installed. My guess is maybe $20 bucks a month. I was surprised as I expected a big spike in electrical use, but I just don't see it.
Obviously, it has an insulated cover..
One downside is that you have to drain and refill it every 3 or 4 months. But it makes cleaning it pretty simple. Not at all like a pool that is open to the elements.
I bought my hot tub used. It was about 10 years old and all original. The only problem I have had is because of stupidity... I drained it with the power on and lost the circulation pump. Cost about $300 bucks for a new one. Other than that it has been working fine.
I converted mine to a saltwater spa, so now it is as easy to maintain as my saltwater pool...
One thing to keep in mind that most of them require 50 or 60 amp service, with circuit breaker box near the spa. I installed my own, but I could see that costing $1,000 give or take, depending on where your main Circuit Breaker panel is located.
Thanks for posting,
Jim R.