I have been A/B'ing between the two apps for a while now & the more I switch back & forth the better the Nav views look.
When I open the street view in >
Google Navigator < it opens in full screen automatically & it must be a higher resolution image than the BB version because it is noticeably less grainy etc.
GN is pretty slick (the spoken turn by turn GPS routing works well), but it does have a few bugs in it & I don't recommend that people buy it at this time.
~John