you may want to wait a bit longer, since it is said to be updated very soon.
I have it and also Sony Nikon 70-200mm f4G lenses and I compared them side by side many times, in absolute term the Canon f4LIS is still a good lens but it shows its age compared to the Sony and the Nikon,espeically to the Sony.
and imho, the Canon f4LIS and Nikon f4VR are overpriced compared to the excellent Sony 70-200mm f4 SSM , the Sony comes with tripod mount and it is about 100US cheaper than the optically inferior Canon f4 70-200mm and the Optically as good but heavier Nikon..
I tested them all on my A7R and see the differences, the Sony was clearly sharper than the other 2 at 70 , 100, 135mm wide open , but at 200mm end , the Nikon was the better lens at f4 , but stopping down to f6.3 , the Sony becomes better than the other 2 again. I also compared the build quality of the 3 lenses, to me the Sony seems better made lens but a bit bigger than the Canon, the biggest one is the Nikon f4 and it is a bit longer than the Canon and the Sony. But honestly I prefer the look of the Nikon lens since it is black and less conspicuous in public. but if do not care about the color of the lens, but only optical quality and AF accuracy , then the Sony wins hands down here. and after comparing the 3 , I am quite sure, the Sony and Nikon 70-200mm f4 are quite a bit better than the Canon one, and I am sure Canon must update it with better IS and better anti-flare coating very soon to be competitive. the Nikon has almost 5 stop effective VR , and it focuses very very close, so personally I do not buy the Canon f4 70-200mm IS lens now , and I do not need f2.8 any more in this range(I use the Zeiss 135mm f2 APO instead). So if I need the best 70-200mm f4 zoom now , I will go Sony or Nikon. If you can wait , wait a few months , I am quite sure we will see a new 70-200mm f4LIS lens from Canon at Photokina(it does not mean we can actually buy it very soon , though).
All that having said , the best 70-200mm zoom is the Canon 70-200mm f2.8LISMK2 USM lens.