Recently, I have been considering the purchase of 70-200mm f2.8 lens. However, there are many brands that has this lens, example sigma, nikon and tamron. I am a nikon user. However, getting nikon's 70-200mm f2.8 isn't cheap. There are many alternatives from sigma and tamron. I am unsure of which 3rd party lens I should go for. I appre70ciate if any of you people could tell me which lens has Sharper image quality and of course your valuable experiences.