Catholicism was only good in 1.7 if you had 4 or so controlled cardinals and a good relationship with the pope. Every other religion is better to start with and depending what you want do Orthodoxy is decent at one end of the spectrum or the other, but not mind blowing.
Now, I think being the only major Catholic country is really the way to go, as soon as the revolutions start, pick up defender of the faith and ride out the storm, expanding and converting like crazy. Please don't complain about the Papal system until you are a major country seen as the guardians of Catholicism, like Spain, France and Portugal were in our past.
As a member of the HRE looking to much it all up, pray for revolution, as a minor nation the Papacy is not your ball pit.