Still the beginning of the trade season but we have had some most excellent conditions the past weeks and today we still have 40 knots. Check conditions at pozowinds.com for Gran Canaria.
I would say your chances of good winds in the canarias would be good for your period.
As for which island I would agree that Fuerteventura has the best selection of different spots. Waves on the north coast (Majanicho and other spots), bump&jump and some waves around Corralejo (Flag and Glass beach) and the infamous Sotavento which has strong (but very very gusty) wind and flat water both in the lagoon when full or just outside the sandbar.
Gran Canaria is a bit more hardcore with stronger winds (add 10 knots+) and rocky beaches. The sandy beaches in the south do not work with the summer trades. If you can handle 40 knots, rocky launch, a bit of a shorebreak and large blown windswell GC is really good
As for Tenerife I cannot say but for all I know only El Medano really works there.
Their season is over windwise. The trades move north for the summer and it will not be as reliable as the canarias this time of year.
Winds about as canarias. Enormous sandy lagoon and some nice outside stuff also. Besides kitesurfing not much (read nothing) to do. If you are travelling with non-sailing companions forget about it. Best way to get there is via Gran Canaria. Saharafly departs twice weekly for about 230 euros return. Good in combination with Gran Canaria and remeber you can also get by ferry from Fuerte to GC easily. 4 hours from Morro Jable to Las Palmas.
Someone else should probably comment on this as I have only sailed there twice for a week. Levante nice and strong but a little gusty. Nothing like Sotavento though, much more stable. Poniente ok but will see the beach packed with 1000's of crazy newbies flying all over the place.
Cannot say, never tried.