With the next hardfork coming, either option is about the same.
You'll be able to power down more quickly when you want to withdraw, so it won't make much of a difference as far as transferring it out.
On the other hand, if you power up, your vote will have more influence and your curation rewards could be larger, so that's a plus for the power up.
I haven't turned any of mine into Steem Dollars, because SD stay around the same value, whereas STEEM had the potential for great increase.