What does your roster look like? As long as you have G3 and a GP Usopp, you should be able to take down Mihawk.
Laboon/Vivi will only allow you to clear 3 raids: Mihawk, Monster Chopper, and Garp. I wouldn't recommend farming Vivi because you will need to evolve her twice then get her to a high level. It'll be easier to ask one of us to put Vivi up as captain. You could use Laboon against Blackbeard but you'll need despair level 1. If you think it's worth it, then you should farm him. If you do get him, do not level him at all. You want to have the lowest amount of health possible.
Depending on where you're at in the story, I would farm Crocodile and Enel. If you're not even that far, I'd say just run fortnight islands until your P-lvl is higher, there's not that many good units before Alabasta arc.