I'd expect Crete to be very very hot (40C+) in the height of summer, whereas Lanzarote will be more like high 20s/low 30s. But the Crete sea will be warmer.
However, that Lanzarote hotel is quite a way outside Playa Blanca, 30-40 mins walk along the front to the marina, main town and main beach areas - the little beach you can see on google earth isn't up to much. So you'd have a long walk to a proper nice beach, or need to drive.