Graphic theme is preferrable in that there's less potential for repetition inside individual sets - that's the big criticism I see levied against Touched!. However, Smooth Moves doesn't really have "gimmick" sets - new ways to hold the Wiimote are progessively introduced, but a given character can still have a "form" from a previous set, and there's no clear theme to each characters beside Wario and 9-Volt's
OTOH, the original WW has the opposite problem in that there's quite a few clone microgames between character sets, just with a different coat of paint. It's most obvious with the "Mash A as fast as possible" ones, but there's a few repeats of "press a button to have a flying object drop on an immobile object below it" and "press the D-pad directions indicated on the screen" too.