I think Chris Algieri, Viktor Postol, Mauricio Herrera, etc would always give Danny Garcia problems, because he's not that good of a "pure" boxer and he's slow in his punches and feet.
Boxers like those listed above would give him trouble, while on the other hand, people like Keith Thurman, Lucas Matthysse, Ruslan Provodnikov, etc would be easier fights for him due to the fact he's a really good counter puncher and ALWAYS catches over aggressive fighters with the left hook from his mom's side of the family with perfect timing.
I know it sounds weird when you look at the names, but the evidence is there. You cant really beat Danny Garcia by going toe to toe slugging it out with him...he'll take your punch and KO you. He CAN be outboxed though.