This could be an exam question in disguise
Anyway, don’t buy the Freixenet or codorniu dross.
There are some very good single vineyard Cavas in the Parajae Calificado and the recently formed Corpinnat group of growers.
The key to good Cava is pick early, with a yield of 48hl/ha if you leave grapes like Xarel-lo to get too ripe they get those nasty burnt rubber flavours.
Sweetness depends on dosage sugar levels. Brut or lower will be dry.
Give me a day or so and I will list some specific suggestions.
Good Cava is dry but not high acidity. There are notes of fennel and herbs along with lemon and autolytic notes
In the past the mass produced stuff only had 9 months on lees but reservas and gran reservas have 15 and 30. Some go for 36 others now do 60. So those autolytic notes really come through.