@KyonSmith:
There's a storm coming. Better hide away… :ninja:
Personally, I don't have any FZ nor Grandline, but they are almost the same price as the Grandline series. Figuarts prices vary depending on the size of the figure. Grandline boxes are equally sized and equally priced.
In terms of quality, everyone will shout at the same time Grandline Series. I do agree, but Grandline have a few weird faces, especially Luffy and Nami TS. Others like Roger, Shanks and his crew, and Usopp look okay. But if you are not a hardcore quality fan and want variety, then Figuarts is your choice. They have lots of characters and more to come. At the moment, Grandline features medium-small sized characters.
Other points to mention is that for Figuarts Zero, the final product is almost never as good as the initial prototype (Ace is the only exception so far, from what I've heard). For the Grandline series, they usually improve from the initial prototype (GLC Hancock is a good example; compare what her eyes looked like in the prototype to what they are in the final product: http://myfigurecollection.net/item/72556_one_piece_boa_hancock_the_grandline_children_vol_2), but like Kyon mentioned, they sometimes don't (TS Luffy and Nami, from what Kyon said). The Grandline series also doesn't have as many characters as the Figuarts series (there have been multiple recolors of Luffy and Sanji as opposed to giving other characters like Crocodile and Smoker a chance; those two are up to plate for Figuarts, with Crocodile being already available for preorder).