I can only comment on the Canary Islands.

Tenerifa and the other large islands is fine if you like resorts and the package tour crowd. On Tenerife, the small town of San Andres has some excellent restaurants.

If you are into a bit more "seclusion" and don't mind self-catering accommodations, I highly recommend El Hierro. Much of the island is given over as a UNESCO Biosphere and so the island is largely undeveloped. The people there are lovely (more inclined to speak German as a second language than English though), the food is on the rustic side but delicious, and the landscape is amazing. There is supposed to be some good scuba and snorkeling there as well. If you are into hiking, you will be in for a treat.

As an aside, virtually all of the beach sand on the Canary Islands is imported from the Sahara.

I hope that's helpful.