I have to agree that if I could have one or the other only, I would choose honesty. But, it was not so long ago I might have made a different choice. The honesty of others on this board has sometimes forced me to be honest with myself. And after being dishonest with myself most of my life, that was incredibly painful. There is no easy, painless way to grow, unfortunately.
Having said that, I also think that both honesty and compassion are very subjective. My truth may not be your truth, nor does my idea of compassion always match what others consider compassionate.
I can say that in two years on SR, the times I have witnessed malicious or ill-intentioned posts have been extremely rare. On the other hand, I have seen quite a bit of hostility toward opinions that people don't want to hear. And I have been guilty of both expressing unpopular opinions, and reacting angrily to those I don't agree with. Just more proof that none of us would be here if we didn't still have things to work on.
L