It depends on the scoring system and the strategy you are using. If it's a roto league, I'd take Soriano, because he is a guy that can get you a .300 average, 120 RBI, 100 runs, 50 SBs and 40 HR. If it's a points league or a head to head league where you are punting steals, then take ARod.
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.
Taking a SS in the second round is a good idea, but if ARod, Nomar, Jeter and Tejada are all gone by your second round pick, you shouldn't then go and pick Renteria or Furcal, because they shouldn't really be taken until the 4th or 5th round.