My wife's coworker once told her they had "strong opinions, loosely held". I like the idea generally, but over time, it has struck me as giving the impression of someone easily swayed - either by flimsy arguments or manipulation.
I am not easily swayed (at least I hope I'm not) - changing my opinions with every thing I hear. But, I am also not extremely rigid (again, I hope not) - white-knuckling my beliefs or opinions, desperately holding on in the face of contradictory evidence.
So, I've adopted the variation "strong opinions, firmly held". That is, I have strong opinions based on evidence, which aligns with my core beliefs, and I am open to changing these opinions if there are sufficiently strong arguments and evidence to do so. But my core beliefs are universal and strong enough to support those types of change.