Lens advice

I am looking at 2 lenses to go on my Nikon bodies (D300, D200, D2h). The first is a used Nikon 400 f2.8afs and the second is a new Sigma 500 f4.5. Interested in opinions on these with and without tc's. I am also aware of the weight difference. The cost is for the two is a push.
Thanks for the responses,
Todd

Todd I would have to go with the Nikon lens !! Quality difference aside it will focus a lot faster.

Glad you are well aware of the weight difference !!!

Thanks Al, I was leaning that way but I thought I would ask. The new vs used was the biggest thing on my mind.

Todd