After a certain age people stop asking you what your favorite dinosaur is, and I think that's sad.
My current one's the Anchiornis, because it's in the same clade as birds so it's in their family tree, and it really looks like a prototype of a bird. It had 4 wings for example, but it already looked very birb-y:
(Figured I'd just turn an earlier comment into an actual post because why not)
Stenonychosaurus (née Troodon) because as unlikely and silly an idea as it was I always found the whole "how intelligent could they have become if they hadn't gone extinct" thought experiment fascinating.
I also have a soft spot for Struthiomimus just because it's such a fun word to say.