Aqua park question?

Which one would be best for my 20 yr old Grandaughter and her boyfriend, the Quesada one or La Siesta?...Thanks.

La Siesta is definitely for the younger kids although it does have one big slide and a couple of small ones.
Quesada is fine but, again, not really for 20 year olds. The main pool (the only one that's not for kids) gets so busy you can't do anything but walk around. La Siesta does at least have one pool you can swim fairly easily in.
The best one for that age would be the Torrevieja water park, Aquopolis.
If using Aquopolis, buy the tickets on line or with a discount coupon as you'll save up to 10 euro per person.

Yes agree with marcliff a lot more to do there.

Why not book them onto the daves coaches trip to the massive one at benidorm, probably a lot more suited to thier age group and not much more expensive for a full day out

Definitely Aquapolis or Benidorm, the others are for children