I should've wrote 'which one would be good to see? As in the movies'

Ninjago Canon movie.

Oof

Batman. I'm speaking as a big Batman fan who hasn't ever watched Ninjago the show, though I plan to, or bought any of the sets, though I might if I find I like the show, so I won't pretend to be objective here, but based on what little I know it feels like Batman has more goofy material that's ripe for a comedic take, while Ninjago, though it's possible to do a funny movie based on it--and I did really find it funny--does not.

The jokes you can tell about Lloyd and Garmadon's rocky relationship, are jokes you could tell about any father and son duo on opposite moral sides; likewise while I guess a giant monster rampaging a city does fit with the fairly Japanese theme of the property, it being an ordinary house cat who is only a kaiju in comparison to LEGO figures feels like much more of a general LEGO joke than a Ninjago joke. It also leans on viewers having seen The LEGO Movie and knowing that in-canon, these stories are really about toys being played with by real people.

Batman is more primed for a sort of humor that feels uniquely Batman. Because modern audiences are mostly aware of the brand as some shade of dark and gritty, Batman doing things you wouldn't expect him to is a seemingly endless well of comedy in and of himself, but The LEGO Batman Movie went above and beyond by actually making all of those goofy behaviors feel genuinely grounded in his backstory. Furthermore, though, the film milks the silly peripheral aspects of his universe, and again, it feels like there's a lot more of them than Ninjago by very definition. Ninjago just turned ten. Batman has been around for over 80 years, and as stated above, that recent audiences have been treated to a mostly dead-serious version of Batman, with a lot of the exotic bits ironed out, the same sort of juxtaposition humor that applies to Batman himself also applies to Gotham as a whole; people can giggle at a villain shooting people with ketchup and mustard for the same reason they giggle at Batman swimming with a dolphin, because both run contrary to expectations.

The one problem I have with The LEGO Batman movie, is that a lot of those amusing bits of Batman's own lore were tucked off into the margins in favor of a mass crossover. I have nothing against seeing Batman on Sauron, but that's not the movie the trailers promised. I would like to see a Batman movie go all in with just Batman characters; there is more than enough to work with.

@BaronBahmo very good point. I havent watched the whole Batman movie, but yes the crossover almost wrecks the movie. Its called 'Lego Batman Movie' right?

If you've seen, some animated Lego DC movies have been made, and they're just DC, no crossovers. Maybe the next Batman could be like them perhaps