Option 2: Tamron AF 70-300mm f/4.0-5.6 SP Di VC USD XLD Lens
- Great price
- Good sharpness
- Works on full frame and crop sensor
- Not as good build quality as the Canon
If you can get the Canon 70-300 in your price range, this is the lens for you. But be sure to use this link because there are multiple versions of the Canon 70-300. Amazon has several used copies of this lens to pick from, and I've usually had good luck buying used lenses.