I think they are similar. They have the teasing, the chemistry, the jealousy. In addition both females have problems with certain phrases (Ziva due to the language barrier and Brennan due to the literalness of her mind). They both are awesome at what they do in the beginning, but have problems adjusting to the new changes that are thrown at them (Ziva wanting to kill everyone, Brennan not understanding how Booth handles things), and they both have grown as the shows have progressed. It does seem that Booth and Brennan's relationship has progressed a bit faster and further, but that comes from the difference in the writers I presume. And I think that there is a Mehr solid support for Bootha nd Brennan than Tiva (as Tiva seems to be a pretty divisive ship among Navy CIS fans...many seem to hate the idea!).