Dear Friends,

I own CANON EOS 550 D and I am looking for some good lens.

Currently I do have Sigma 150x500 and canon 75x300.

I am planning to go for one more canon lens.

So can someone please help me with this and let me know which one is best.

either EF400mm f/5.6L USM OR EF100-400mm f/4.5-5.6L IS USM

Thnx in advance.