Nikon 300mm VR 2.8 vs nikon 200-400mm F4?

I'm using D700 and have nikon 300mm F4 (optional with 1.4 TC) at the moment but i'm not pleased with the results.
I'm considering buying a new telephoto lens nikon 300mm VR 2.8 or nikon 200-400mm F4
what will be the best choice? , I attend to use converter as well since it should be using for nature and birding.

the question her is quality and functionality vs money

I expect the 300mm f/2.8 to be costlier but faster and produce better picture quality. The 200-400 would be more flexible but slower. If you use both with a converter, picture quality would go down definitely. Personally, I'd go for the 300mm f/1.8, get some camouflage suit and a large Coleman for the long wait in the woods.

The 300mm f/4 is a good lens with a poorly designed collar. If you're using a monopod or tripod, perhaps that's the issue. Kirk sells replacement collars. If you are using a tripod, the stability of the tripod itself could also be an issue. 300+ mm requires substantial support… A Gitzo 3 series or similarly chunky Manfrotto/ Feisol/ alternative, combined with a large Markins/ Kirk/ RRS/ Acratech/ etc ballhead and optionally a Wimberley sidekick for a gimbal-type head. For stationary shots use mirror-up and a remote shutter release (when you're shooting at 400+ mm, every bit of technique matters.)

The 300mm f/2.8 version is better than the f/4 version of course, but at a considerable price premium. I've seen some impressive results with the f/2.8 VR ll version even in combination with the TC 2 lll. If you have the budget, that's your lens - forget about the 200-400mm.

You could also consider getting a D7000.It's only a stop worse than the D700 at high ISO and the DX crop factor gives you an instant 1.5x magnification by placing 16 megapixels in the center of the frame. And/ or skip to a used (manual focus) 400/500mm lens.

The problem isn't really functionality vs.money. You know what lenses will work best, and they all cost a fortune. The question is how much you're willing/ able to spend.

Nikon lens reviews: http://www.naturfotograf.com/lens_tele.html