Of course, having both—more fluid animation and a more detailed art style—would be the ideal, but since the Pokémon anime does not have the same budget as a Disney or Studio Ghibli film, that's not going to happen. Personally, I prefer more fluid animation over a more detailed art style. A more detailed art style is nice, but it doesn't lend itself as well to fluid animation, resulting in frequent use of stock footage and/or stiff animation.
One thing I appreciate the most about SM is the fluidity of the animation; and if that means the animators had to soften the lines and simplify the character designs, then I'll take it. In a still visual medium such as manga, the detail of the art style obviously has greater importance. But when it comes to animation, the quality and fluidity of the animation has priority over the detail of the art style, especially in an "action" series—and by that, I mean a series where there is a lot of movement, not necessarily actual action scenes.
While XY's art style was more detailed than SM's, the animation was stiffer and there was more frequent use of stock footage. The animators hid the stiffness well with dynamic camera angles and flashiness, but the stiffness was still there. It was most apparent in the human characters, who didn't really move all that much, especially outside of battle.