Ever Oasis IP is owned by Nintendo? Grezzo is independent, although they mostly work for Nintendo consoles, right?

Besides that, Xenoblade for me. Splatoon is great and fun, but Xenoblade is better. I hope Xenoblade 2 is more like the original, not like X.

Xenoblade, followed closely by Splatoon.

I enjoyed both Xeno and Splatoon.

Splatoon is the best for me.

Xenoblade/Splatoon. Can't decide. It'll depend in their sequels this year.

Ten years....???

Then Splatoon...

15 years... Pikimn!

Not really, it was from the Famicom days.
See Famicom Wars.

If "Maker", becomes a franchise, then I'll definitely pick that.

I'm not even sure if I've played a Nintendo IP the last 10 years enough to even come up with an answer!

I adore ARMS' concept! Never been so thrilled by a fighting game in years.

I really hope we'll see Pikmin 4 soon enough.

Xenoblade, and also Captain Toad, which isn't in the poll. Even if we go by his first appearance in any game (Super Mario Galaxy), he'd still be less than 10 years old.

P.S. Some other ones not mentioned in the poll: Pandora's Tower, Wonderful 101, Captain Rainbow, Endless Ocean, Hotel Dusk, Disaster: Day of Crisis, Style Savvy, Art Academy, Tomodachi, Pushmo/Pullblox, Steel Diver, Boxboy, Code Name: S.T.E.A.M., 1-2-Switch, Tokyo Mirage Sessions. Pretty sure Nintendo owns the IP for those.