Kinds with big parts that don't clog pool filters, are easy to clean up.

What zone are you in? 7? or 6? If zone 7, then 7A or 7B? Makes a difference with plant selection. what is your normal lowest temperature in winter?

Do you want evergreen or deciduous?

Wet area ? or with good drainage? Full sun?

20 feet tall is very tall! and anything growing that tall will likely become very wide over time. Are you willing to trim annually? What about fence maintenance? (painting, staining, etc.)