I would go with the 9800GT if only for its legacy. That thing was a beast of its time.
The 9800GT was actually just a rebranded 8800GT from the gen before, but because it was so powerful there was no competition to it, so Nvidia just renamed it. It eventually was beat by the 9800x2, which as the name implies was just two of the put together on the one board.
Though this was 2007/2008, by modern standards its quite weak.
Still got my old 8800GTX on a shelf, what a beast!