^^
While both characters are laid back and friendly people, I find Yui's thought process is easier to pin down; bribe with her cake and she'll do anything!
Yui can also accomplish a lot when she puts her mind to and definitely has musical talent.
As for Tylor, I've finished the entire series and I still have no idea what goes on in his head. Tylor never offers a clear explanation for his actions either and most of his actions can be taken as either clever plans/improvisations or extraordinary luck or possibly a mixture of the two. His crew seems to feel the same way but regardless of his actual intelligence, there's no doubt that he's reliable.
In short, I think Yui's relatively straightforward and Tylor is enigmatic.