There are three lens in question which fall almost same price category. Please comment on your choice and why you would vote for it.
Canon EF 100-400 L IS USM - Most suggested wild life lens.
Pros - The range, sharpness through out above 200mm
Cons - Push-Pull can suck in air and in humid areas such as Kerala it will easily attract fungus. There by limiting the lifetime to 3-5 years. Once can use a digicabi or similar setup as a work around. Cannot use Tele Converters.
Canon EF 400 5.6 L -
Pros - Lightweight, Sharpness
Cons - Build and IQ wise I do not have anything to worry, but the main disadvantage is the aperture on the slower which will limit and you won't be able to use the Tele converters. The lack of IS, as a workaround one can easily carry a monopod.
Canon EF 300 4 L -
Pros - Same as above and you can use the Tele Converters(If I'm not mistaken)
Cons - Compared to the above lens we are losing 100mm focall length.
The Big reason where I had chosen 100-400 as my first tele is the range available for the lens. In the wild whether that will be a factor or not is another thing, but it surely will count when you are clicking something closeby.
The Reason for considering EF 400 5.6 is the price and IQ it brings. But in this case we may loose the close by subject(how much a loss that would be I do not have a idea).
The Reason for considering EF 300 4 is the bigger aperture which will give an option to use tele converters if desired for the cost of 100mm.
Please pour in your thoughts as well.