Which Nikon Lens to Purchase? 70-200+Tc 1.4 or 200-400?

I Primarily shoot Birds in flight, mammals and people's portraits. I'm looking for a best possible combination…

Added (1). I use a D5000, and my current lenses are the kit + 55-300 VR.

My Primary need is to step up to a higher aperture + decent zoom combo.

Since you have to ask, you definitely don't need a 200-400.

Rent a 70-200 & a converter and see what you think. Borrowlenses, lensrentals etc are good places to rent from.

A Sigma 50-500 might also serve you well.

I'm assuming that you're using a crop-sensor DSLR? If so, you need to account for your camera's a 1.5X crop factor.

I would not recommend the 70-200mm 2.8 if you wish to use a converter. I have read about tests where this lens performs poorly against similar rivals when using a converter. I've used a converter on mine and it did not focus very well.
It is a super lens on it's own, however.

The 200-400mm f4 is expensive, but a better option if you can afford it.

Myself, I use a 300mm f/4 which works superbly well with a 1.4x converter. There's little, if any drop in quality when using this combo. It is a cracking lens which I bought new (with converter) for £1200.