Your second round pick would fetch a very nice player, unfortunately you aren't in a good position to trade it, as you would be without a pick for the first 4 rounds. So I would throw that option out.
From your current roster I'd be quite tempted to keep M. Koivu, but I think that would be heavily pending on what goalies you think will be available in the second round, versus the quality of players available. If goalie is very important to you, than Holtby becomes the best keeper option from your current roster, and if you have no desire to keep him beyond this season, I would look towards your other option.
If your going to keep a goalie, I would trade your 7th round pick for Anderson. For a single year he should be better than Holtby even at the price of a 7th rounder, and with neither likely to be keeper options the next season, I take Anderson.
Your 5 keepers would be Tavares, Ovechkin, Hall, Benn, and Anderson.
I definately would like to get a quality keeper goalie and am focussed just as much on the long term as next year. Why don't you see Anderson or Holtby as a potential keeper beyond this year? If Holtby has a good year won't he be solidified as Washington's number 1?