My experience with randoms in HR and early G-rank is that they mount early and often, so there's a ton of chances to use crouching fire. And it is glorious. For solo play, you can roll into crouching fire by pressing X during the rolling animation which might give you some opportunities to use it, but in general it's too risky for solo play unless you really know the monster's patterns.
For Normal, the Najarala and the Molten Tigrex guns are both pretty good. For Pierce, I like the Plesioth gun because you don't need to use Recoil Down with it, and the Daora and Ukanlos guns are good, too.