First of all we're talking different classes of lenses here. 70-300mm, 80-400mm, 70-200mm + TC, 200-400mm are all wildly ranging lens/price classes.
I have used the non-VR 70-300 and found it appauling, soft and full of CA. Especially at 300mm which is where you'll spend most of your time with wildlife. It may be better in the newer model, but for it's class, the 300mm end will always be crummy.
I have owned an 80-400mm for a couple years and its the lens that got me started in wildlife photography and it's brilliant! The focusing is a little slow and noisy but only when initially finding the subject, after which it tracks quite nicely and have shot many birds in flight with it. Trust me, the 400mm end makes all the difference and it can be quite sharp.
the next step up in price is the 70-200mm + 1.4x/2x TC's. This lens is amazingly sharp (noticably better than 80-400), but 200mm is nothing for wildilfe. With a 2x TC's you will lose light, focusing and sharpness beyond the 80-400mm. It is also a little bigger and heavier than the 80-400 especially with the TC's.
I have not shot with the 200-400 but i'm sure its amazingly sharp and fast. Personally I now shoot with a 300mm f/2.8 AFS/VR + TC's and my 80-400's gathering dust (but I haven't the heart to sell it...).
So, it really depends on what your budget is, if it's tight, get the 70-300mm, otherwise I'd get the 80-400mm and only reccomend a high end lens like the 200-400mm if you're really serious about wildlife and lugging that weight and price tag around. It will require a monopod to shoot, as does my 300mm. Cheers,
Chris