I think for me, it's tied between Serebii and Bulbapedia. I use both for information, though it mostly just depends on my "mood." I will say that Bulbapedia looks much nicer than Serebii, which looks like it was designed in 1993, so I might go to Bulbapedia a little more often.
I do visit Smogon regularly as well, but not as much as Serebii and Bulbapedia.
And I'm surprised Marriland is still a thing... That and Pokejungle.
THAT'S MISS FUNERAL CAKE TO YOU i disgust myself and everyone around me