Blogging 101: Be a good neighbour

I must write four (or more) comments on blogs to which I have not previously commented. Should I comment on posts that ring true to me, which would be easy?  Should I try to comment constructively on views I would spend a lifetime opposing, which would be hard?  Or should I seek posts in areas where I am currently on the fence, which would be unlikely as there are fewer such areas around, nowadays?