Lens choice is killing me!!!! Help please

I'm having a tough time trying to decide what lens to get. Right now I have a Sigma 17-50 2.8 and the canon 50mm 1.4. These are the only two in my bag at this moment due to selling old gear and getting new gear. I like to shot birds, wildlife and just about any out door stuff. So this is where I'm at. I know I want a 70-200 2.8 but not sure what brand. Canon without OS or the Tamron with VC. If I get this lens first I won't have allot of reach for birds. Now the Canon 400 5.6 seems to be best bang for BIF and will of course do other wildlife as long as its not to close. The next lens seems to be the 100-400 which will give me a wide range for now and allow me to do wildlife. But I here its a little slower on the focus and softer @ 400mm. I will be using the 70D. So my question is what lens 1st. I belive I will be able to get my next lens after this in about 4-6 months, so I just need to pick one to start off with.

The 100-400 was my first L-series purchase and 5 years on I still have that lens and never felt the need to upgrade it. Mine is sharp at 400mm and the extra wider range makes it much more versatile than the 400mm 5.6. Some people don't get on with the push pull action but I find it very easy to use. If you want the 70-200 and can stretch to the MkII 2.8 then you could always get a 2x extender and get 400mm that way and the sharpness wont be far off the other lenses.

the 100-400 is a great lens and honestly, any sharpness benefits the 400 5.6 might have on paper is not really applicable in real world situations (in my opinion, unless you are an extreme pixel peeper). That said, I think the 400 5.6 is a better choice if you are looking for a dedicated birds/wildlife lens. The 100-400 is obviously more practical if you want to use it for other situations. Both are great. Im thinking about adding the 100-400 to my kit at the moment. (I found it to be plenty sharp at 400mm 5.6)

If you want a lens that you can use on lots of things I'd say the 70-200 with your choice of extenders would be a great choice... especially on a crop.

For versatility (near/far:birds/mammal​s) you can't beat the 100-400; it's been my workhorse lens, now, for about 5 years and still producing wonderful shots. It would, overall, be my suggestion for the one to pick up first.

It, of course, works great for still shots, even wide open:

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I wish I had an answer for you, I'm having the same problem! LOL
Just got my 7D in the mail yesterday, so many lenses so many choices. Upgraded from the XS. I've gotten into motorcycle racing photography since several of my friends race. The 70-200 f/4 might be my next choice to swing.

70 - 200 with VC + Extenders.

How about a used Sigma 50-500 OS? Very versatile focal range and a great wildlife lens very comparable to the Canon 100-400L.

I just bought a 100-400 yesterday. I used to have an older Sigma 400mm prime lens, but I found that a zoom is more useful for me at this time. If you are looking to photograph primarily birds, go with the Canon 400 prime.

What about the 70-200 F4 IS

Not NEARLY long enough for most birding pursuits unless shooting from a static blind near a feeder/feeding spot.