Fuerteventura
The main resort is at the top of the island. I don't know anything about it. However, along the coast around the middle of the island there is a new-ish resort town called, I think, Caleta de Fuste. We stayed there a few years ago; accomodation was fine, food and facilities reasonable, but if the wind was coming across the island (i.e. coming across the island and blowing out to sea, as opposed to in from the sea) there was a huge amount of red dust (volcanic ash) and it gave our child a bad chest problem. She was hospitalised for 5 days. Apparently it is quite common when the wind blows a certain direction. There were other children in the hospital with the same complaint and asthma inhalers were selling like hotcakes (without prescription) at the pharmacy.
I don't know how common these conditions are, and I imagin that in the main resort area at the top of the island (where you have water on three sides, it being relatively narrow) it is hardly likely to be a problem. But if you have a weak chest or small children, stay clear of Caleta de Fuste.