I have been meaning to ask this question ever since the private beta started, but now a good example came up.
In this question I have posted an answer myself and Bernhard has posted an answer recommending a different vector drawing program. I think the answer is well written so normally that would mean I would upvote it. However, I disagree with the recommendation, I think the program he suggest is not as good as my own recommendation, by which logic I could choose to downvote it.
What should I do? Vote on answer quality (up), vote on agreement with the recommendation (down) or should I refrain from voting in this case?