Which is the better lens for wildlife, sport action canon 70-200 is usm ii series L or Canon 100-400

Question

Which would be a better for wildlife and sport action Canon 70-200  mm is usm ii serie L f/2.8 or Canon 100-400 mm f/4.5-5.6?

Answer 1

On what camera? It makes a big difference depending upon whether you are using full frame or a crop camera.
Also depends upon the particular sports and type of wildlife most commonly involved, how much reach you might need.  Outdoor, daytime sports vs indoor and nightime sports is another key factor.
On a crop camera a 70-200 is generally a lot more usable than it is on full frame, for sports and wildlife. An f2.8 lens and 70-200 might be ideal for indoor sports even with a crop camera. It also might be plenty for large game that can be pretty closely approacted. But for small and more shy wildlife, sports on a  larger playing field, you'll more likely need the 100-400. But as an f4.5-5.6 lens that's going to be more of a daytime-only lens.
The 100-400mm is unusual in that it's a push/pull zoom. This can be particularly fast to use and makes the lens popular among photograhers shooting fast moving subjects such as birds in flight and air shows.
If you give serious consideration to the 70-200/2.8 IS II in combination with teleconverter EF 2X III, I'd suggest renting and trying them toghether first. The reason is that a stronger 2X teleconverter has more effect on image quality than a weaker TC. The specific combination of the 70-200 Mark II lens and the 2X Mark III TC is pretty darned good.... better than the combo earlier versions of each item.  But whether or not it's up to your expectastions is a judgment call only you can make. So it might be wise to rent before you buy, just to be sure. 
If instead you start to take a hard look at the 100-400mm, once again you might want to rent it and give it a try. Some people really like the push/pull zoom design. Some don't. (I'm one of the latter...  but to be fair this is largely an old  prejudice from trying to use that type of zoom in the past, long before IS. I always found push-pull zooms hard to get a steady shot with.... But the 100-400's IS goes a long way toward solving that problem.)
And those two really aren't your only choices.
Personally I use a pair of crop cameras (7D), most of the time one fitted with a 70-200, and the other fitted with a 300/4 IS, sometimes in combination with an EF 1.4X II teleconverter. Or, when I don't need to be mobile and can set up a tripod, I'll use a 300/2.8 IS, both by itself and with EF 1.4X II or 2X II teleconverters.
Another possibility is two lower cost lenses... such as a 70-200/4 IS in combination with a third party lens such as the Sigma 120-400 OS or 150-500 OS. Those lenses are considerably less expensive than the 70-200/2.8 II and the 100-400, respectively. You might be able to afford both and still find they meet your needs very well.
I use the 70-200/4 IS, as well as a copy of the first version of the 70-200/2.8 IS, and they are excellent lenses too. No doubt about it, the 70-200/2.8 IS Mark II is top of the heap and exceptionally good... but rest assured those other 70-200s are no slouches.
If using a full frame camera, for large field sports and more distant, smaller wildlife.... better start saving up. You're going to need one or two of the super telephotos, such as the new EF 200-400/4L IS 1.4X that I'm saving up for!  
p.s. By the way, if not already doing so you might want to try Back Button Focusing. It's a very popular technique among sports/action and wildlife photographers. I've been using it for years for virtually everything I shoot, and can't imagine using any other method now.
Alan Myers
San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7D(x2), 50D(x3), some other cameras, various lenses & accessories
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