All the Canaries give you good riding with reliable weather on generally good roads. Gran Canaria is the best for me - you can get up to Pico de las Nieves by several routes; and if you want challenging, the 200k+ ride round the circumference is still my all time best ride. The island has every terrain from lush banana fields to rocky desert and that NW coast road above the cliffs is just spectacular.
The Algarve? Nothing huge, but lots of quiet rolling terrain behind the coast, and allegedly the sunniest part of mainland Europe.
And there's always Mallorca, which has miles and miles of great scenery, especially along the Tramuntana. It will still be hot in October but I suppose you aren't guaranteed a dry week. Have you done Sa Colabra, or the ride up to Lluc from Pollensa?