[richardpcrowe]

The 70-200mm f/4L IS lens is probably the best general purpose long lens manufactured by Canon! The 100-400mm IS lens is also a good lens but, is IMO more specialized than the 70-200mm f/4L IS and is also not quite as sharp as the 70-200mm f/4L IS. The 100-400mm IS lens should be considered for wildlife when you absolutely need longer than the 200mm end of the 70-200mm f/4L IS! The 70-300mm DO is (again IMO) not quite up to the IQ standards of the 70-200mm f/4L IS.

I switched from the 70-200mm f/4L (non-IS) lens to the IS version and I have not looked back. I use the IS lens 3-4x more often than I was ever able to use the non-IS version because of the increased ability to hand-hold the lens due to the wonderful IS.

I also occasionally use my 70-200mm f/4L IS lens along with the Canon 1.4x TC. This gives me a 320mm f/5.6 lens (512mm equivalent) with very good imagery and ability to autofocus.

The 70-200mm f/4L IS lens makes an excellent partner with the newer 17-55mm f/2.8 IS lens. The focal range between 55mm and 70mm that is missing from this combination is not all that critical. The combination of the above two lenses will give you excellent imagery and almost instantaneous AF.

Although, this lens combination is not inexpensive... It is (IMO) one of the best two lens combinations available. The combimation works wonderfully with one body but is even handier when each lens has its own body. That way, you don't have to switch lenses in the field and incur the problems connected with lens switching: 1. missing a shot while switching, 2. dirty sensor due to switching and 3. physical damage to the lens (dropping, etc.) while switching.