« on: September 19, 2014, 06:59:23 AM »
You are spoiled for choice.
If you sit in a hide (blind) and use a tripod and have lots and lots of money, the 600mm f/4 II or the 500mm II are simply incredible. The I series are nearly as good, much cheaper but heavier.
If you don't mind less reach but more flexibility and be able to hand hold, and also have lots of money, the 300mm f/2.8 II plus 1.4 and 2xTCs or as seems likely the brand new 400mm DO II plus TCs are outstanding. (I don't get tired walking with and holding the 300mm f/2.8 II). The series I 300/2.8 is not as good with the 2xTC but still amazing native or with the 1.4xTC.
If you have much less money I would recommend the Tamron 150-600mm which is incredible value and as good as the 100-400mm L where they overlap and has the extra reach and better IS (I am very pleased with mine). The 100-400mm L is a very good lens and small, but you must check it out first as there are some bad ones out there. The new Sigma 150-600s are as yet untested, and the old 150-500 is not good at 500mm. The 400mm f/5.6L is a nice lens, very sharp and fast focussing but you are limited in its use as it doesn't have IS. The 300mm f/4 IS is very sharp but it is a bit short and it is not as sharp with the 1.4xTC as the 400mm native, but again it is very good value and has IS.
I started with the 400mm f/5.6 L, loved it, but changed to the 100-400 L as it was more useful to me with its IS and zoom, then did the 300mm f/2.8 II, which is my favourite, and now use the Tamron for travel as it is very good and more portable.