Well, Florida has been mentioned and so has San Diego.
I grew up in central Kansas. Then lived on the East coast of Florida for several years. Compared to Kansas, thought Florida was great, then moved to Southern California (Orange County which is not too far removed from San Diego). Florida is OK and does not have a state income tax but I did not care for the humidity and bugs and hurricanes. California was much more pleasant weatherwise but there are a number of reasons now to avoid California if there is a choice and we made that decision to leave California. Smog is not so much of a problem anymore, but it is still there in the populated areas like Orange County and even San Diego. The real problems there now are the paralyzing taxes, which will only get worse if California tries to solve its financial problems, the crazy politics (see taxes), traffic which is getting worse in every metropolitan area, earthquakes, fires, mudslides, more taxes and oh, did I mention traffic. We moved from Orange County (CA) 8 years ago to Tucson. Tucson was chosen for a number of reasons. Year round flying, the flying facility here, at the time - a favorable cost of housing, overall cost of living, cost of gas is usually some of the lowest in the country, a reasonable local and state tax structure (at least compared to anything in CA), a great CL community was already here and a number of CL people were moving from the LA area at the time, and the snow birds add to the CL community. As mentioned in another post, we fly essentially year around. There are people on the circles every Wednesday, Friday, Saturday and Sunday, and often on Monday, Tuesday and Thursday. Compared to Florida, bugs are practically nonexistent.
Yes, it does get cool here in the winter. We have had several nights where the temperature was below freezing and we sometimes can see snow on the mountains to the north and east. But compared to the rest of the country, cold is not a problem. Yes it gets hot in the summer and you schedule activities to avoid being outdoors during the hot part of the day. Evenings and mornings are still comfortable. Rain and high humidity does not happen very often.
We are sort of in the extreme SW corner of the country, so proximity to a lot of major contest in the East and Northwest is a problem. However, there are as many as 9 or more contests here in Arizona and Southern California during the year here or are a reasonable driving distance of Tucson.
Altitude at our field is about 2,300 feet. If you can get your engines running here and the airplanes trimmed out, you will be able to fly anywhere in the country with little adjustment (except for some place like Denver).
The only time I have seen rattlesnakes have been in captivity in the desert museum which is near our house and our house is sourrounded by open desert (the Tucson type of desert) and I have been stung only once by a scorpion.
This place pretty well satisfies the criteria listed at the beginning of this thread, probably as well or better than any other location.
Keith