Liver model

Hi,
A general question.
I want to test quickly some expression cassettes which I intend to use
in vivo in mice liver. We have tested them in hepatic cell lines (Huh7,
HepG2 and Hepa 1-6) (transfection) but the potency and efficacy of the
different constructs depends on the cell line (as espected) and is
difficult to make a promoter choice.
Do you have an idea of what is the more phisiological in vitro choice to
do this sort of studies. Primary hepatocytes perhaps?, if so, how easy
are to transfect with conventional methods?. Is there any other option?

Thanks