I would honestly say that Ultimate's speculation was the worst solely because how absolutely nasty it gotten. It was mostly normal, the same old leak like other speculation periods, people casually debate it, and then September happens. New direct, people are hyped, and then delay due to earthquake. Isaac time, right? Isabelle, massive salt, everyone's screaming on the topic of deserving and who deserves to get in, nobody agrees, a box causes even more drama, and then... the Grinch. It just had to be real? I mean, it is Ultimate? Or was it too good to be true? Everyone's anxious, slinging crap at each other, reports of harassment, brigading, all that jazz. And then
It happens
The November 1st direct is live, and the Grinch gets suplexed by Tony the Tiger, and then Plant.
The fandom went nuclear that day, like, far worse then Gemastu, this was a whole different beast of anger, threats disappointments. Claims that Sakurai should be ashamed, all that.
Because of all of that, I would say that Smash Ult. Speculation wasn't fun at all, instead of nice conversations on who might make the cut, it was more like an unorginized political debate. I much prefered Smash 4's speculation.
I do like the DLC talk we have here though, it's nice and quaint, kinda like Smash 4's DLC talks.