hi guys, need a longer lens for shooting mainly birds and wildlife. thinking of buying either the nikon 80-400 f4.5/5.6 VR AFD or the sigma 120-400 f4.5/5.6 DG OS HSM. been down to my local camera shop and had a play with the sigma and quite liked the feel of it, when i asked there opinion on which lens was best they said the nikon but i read a post on here the other day which said the nikon was the worst lens they ever made ! i'd appreciate advice from anyone with experiance with either or both of these lenses. thanks in advance .