Canary Islands

I booked tickets for the first week of april.
I don't think i've enough time to do both Gran Canaria and Tenerife.
So i'd like to have advices on which one is the best to stop by.
Of course i plan to veg out at the beach, bars and restaurants but it seems that both of them are busy enough for that matter.
I heard of the pyramids of guimar, the teide, the national parks.
What else would be worth seeing?