Which (if any) answer should be accepted on poll type questions? A few weeks ago I asked what-are-your-favorite-english-language-tools. I never asked a CW question before, thus I've no idea whether or not I should accept an answer among great contributions.
There has been some discussion on the meta Meta about this, see e.g. this feature request: “Remove 'accepted answer' feature for community wikis”. For all I can tell, no consensus has been reached.
Technically, you can accept an answer on a CW question, so nobody can forbid you to make use of this feature. However, nobody can force you to use it, either. Note that CW questions do not count towards your accept rate.
Personally, I think that since CW questions are, by definition, owned by the community rather than by the OP, the OP can just lean back and let the community sort things out for him. Picking an answer to accept is not only difficult, or even impossible, but it also potentially interferes with the sorting by votes. (Of course, you can always unaccept an answer and accept a different one that has gained more votes in the mean time, but then why bother accepting an answer in the first place?)