Gotta be joop as others have said for the changing details and the dynamic display of its moons. Saturn looks much the same every time I look at it depending on seeing.
I just had look at this poll to see if Uranus had taken the lead yet, no, but one more vote anyway.
Wonder who else voted for this little blue/green fella and why.
Also why is the total percentage over 100% even over 200% ?
That's easy - Saturn will always be No.1 for me! Seeing a fuzzy Saturn in a dismal, poorly mounted toy shop telescope as a kid started me off on this whole astronomy thing.
Second is Jupiter for the detail, Galilean moons etc.