Play either or. Playing one before the other won't spoil the other for you. Pillars of Eternity is (reportedly) a fantastically well done, modernized version of a genre that ages incredibly well, and BG/BG2 are some of the best the genre has to offer (and games, for that matter), of all time. It doesn't matter what order you play them in, you'll enjoy them both unless you don't like the genre.
And yes there were a bunch of dragons on BG2.
WTF dude. Stop with the spoilers!