Maybe not everyone has the same idea in mind when they think of "technical" but when I consider what this encompasses i think of not only technical single moves like shield parry, shine cancell, djc, sh double uar, pivot utilt ect but I also think it should include how moves flow and the proficiency to excute them ie. a characters complexity like tech chase / rushing with ness and then following up for a 0-death or continuing combos / strings with characters like link or fox.
Im not going to go into everything in an effort to keep this short but but I think fox is the clear winner for this title/category. He has an array of some of the single most technical moves which are pretty much vital to his success including shine shenanigans, sh double laser (properly), more of a demand for proficiency, timing, and spacing in everything Including things such as sourspotting aerials and reverse hitboxes. He might not have djc but I'd argue sh z-cancelled aeriels are pretty technical as well.
All of this stuff is pretty technical **** but the craziest thing about fox is your pretty much stringing all of this together non-stop requiring quick percise reactions with a cool finesse touch with probably a higher penalty of failure.
Fox is like a technical marathon whereas characters like yoshi and ness are more like going for short technical sprints.