Based upon the criteria you've indicated (or inferred) the 70-200mm f/2.8 is the way to go. With the recent release of the 70-200mm f/2.8 (Mark II), there's a good chance that there will be some used mark I lens in decent condition popping up for sale on Ebay, Craigslist or Kijiji in the US$800-1000 range. I'd caution against purchasing anything else to save a few bucks - you likely won't be satisfied and it could be tough to resell it once you've come to that realization meaning that you're only that much more in the hole. Wait, save up buy the best.