Soriano, unless Pujols is 3B eligible. Then it's a tough call, but I think I would still take Soriano.
If you have the first pick, then you also have the 16th pick, right? I'd bet you could get either Nomar or Jeter at that pick, so forget Arod and grab one of those guys with pick two. Knowing that also, I would definitely take Soriano because you could still get some decent third basemen later.