Well, definitely being an MVP says a lot about Steve Nash, but to deviate from the most, which I will substantiate, I choose Jason Kidd as the better player. Kidd should have been the MVP in '02 which Shaq even mentioned during his Finals MVP speech saying that Kidd's the true MVP of that season which Duncan questionably won. Kidd didn't win the MVP because he's never the darling of the press, unlike Nash. This is exponatiated by the fact that there are reports of domestic violence towards his wife. And we all know that without the press, getting the MVP is quite hard.
With better supporting players, Nash wins the race. However, with more triple-doubles while having a poor and depleted line-up, Jason Kidd makes a great contention to the claim of who is better; not to mention two trips to the Finals which Nash has never acheived himself. They are both great point guards and are definitely future hall of famers. Also, players will die to play for either point guards. Lastly, their games, though both are point guards, cannot really be compared. Kidd in my opinion is more of the conventional point guard whereas Nash is not so conventional. As a team player, both players are up there. But as an individual player, with much more triple-doubles, Kidd is the better player.
With both of them being great as they are, I guess it just boils down to individual preferences as to who is better.