Lanzarote, much nicer than Tenerife IMHO. There are 3 main resorts the largest and most lively is Puerto Del Carmen, but not a 18-30 type of resorts, more restaurants and bars etc, new town, near casino is quite flat, as is Matagorda, old town can be hilly in parts, something to consider if you have a buggy.
Playa Blanca is slightly more upmarket with a marina, lots of self catering accommodation.
Costa Teguise is a mix of the two. It depends what sort of holiday you are looking for, if you are wanting AI probably CT. For villa/self catering PB or PDC. Loads of reasonable restaurants and bars to chose from.
Lanzarote is quite a small island, hire a car and you can easily get to the tourist spots. The bus service is good to. PDC is 10mins from Arrecife airport, CT around 20mins and PB 35 mins by car.
Lanzarote is full of interesting sights, volcanoes, beaches, caves, zoo, César Manriques’ houses and designs, wine region. The natural beauty of Lanzarote is fab.
The island is full of low rise accommodation, the only high rise hotel is the The Arrecife Grand. I am a Lanzarote fan, can you tell OP, our favourite resort is PDC btw.