If you are playing micro-stakes than I would recommend limping alot. Who cares about building the pot, or narrowing the range when it's likely you'll get an allin bluffer, or caller for the nuts anyhow?

If you are playing higher then 0.25 / 0.50 then in my opinion 20% is too tight. Of course many players can play that range profitably, but I would rather fold AQ to the nits and play 57 against the maniacs.