Yes, Loki is easily in 1st place while Luffy is a distant second.
Luffy has that one page of talking about an “evil Shanks” with one of those guards going for him
Shanks is Shamrock’s identical twin brother
Dragon failed to save Shamrock from the CDs at GV
Blackbeard has history with the Figarlands
Zolo and Scrubo have basically nothing going for them with regards to fighting Shamrock, other than being powerful underlings of guys directly opposed to Imu. And Zoro is already guaranteed to fight Venus
Loki is fine
Goofy will care about an evil Shanks twin, but I don't think he needs to fight him? It's not like they have a particular connection, so it would just be if Shamrock goes for him. But if you want the Gorosei to send someone after him, Sakazuki is still a better candidate for various reasons, and Luffy is probably Like 2 arcs away from beinga PK
Drag-on was radicalized By Garlings actions tho, and Garling is like trying to be the leader against the revolutionary army(read His Convo with the Gorosei, he wants to get things done to protect Mariejois, Which the others don't seem to care about as much)
Blackbeards goal is Imu, made pretty clear, since Garling killing Xebec is basically a technicality anyway. He told Imu he will be back, not Garling, Lol
Being underlings is enough, since Shamrock is Garlings number 2(even if he's stronger)