It's quite a hard choice. I pick Girls on a Mission, since it's the first Lego Friends show that I loved watching after the classic show. It was beautifully animated, I find it funny and entertaining. I also liked the 5 girls' redesigns in this show.
For The Next Chapter, I kinda find the show lighthearted and quirky. I liked the blend of 3d and 2d animations with it. (Shown with the visual effects when the characters express their thoughts). At first, I was skeptical with the show's premise, but surprisingly, it was a good improvement over that terrible Heartlake Stories miniseries...