Which is the best telephoto lens for Canon EOD 5D Camera?

How far do you need to go?

My recommendations for telephoto zoom would be:

Canon EF 70-200mm F/2.8 L IS USM
Canon EF 70-300mm f/4.5-5.6 DO IS USM
Canon EF 100-400mm f/4.5-5.6L IS USM
Sigma 50-500mm HSM

For primes Canon has 100mm all the way up to 1200mm and they should all be good.

Sigma

Get the Canon 70-200 2.8L or the 100-400 L. Both are great lenses. The 70-200 might be alittle sharper but the 100-400 will give you better range.