I'd take Pujols for his versatility. He really helps your draft strategy, as well as pays benefits thru the year. By taking Pujols now, you can grab the best 1st/3B/OF available later instead of having to focus on 3rd.
Giambi would be my 2nd pick. If him and Helton are there, I grab Pujols and hope one falls to me next round.
I owned Sosa for the last 3 years, and he is a great player, but there are many OF out there, and he isn't the top one (Vlad, Bonds). OF is deep.
* Steroid induced record
close, but I'll go Pujols, Sosa, Giambi. But while Pujols is definitely the best player to take, due in part to his versatility, a lot of owners don't see it that way. I had the 8th pick in a ten team draft on Yahoo and was able to get Pedro at 8 and Pujols was still there at 13. If I had taken Pujols at 8, you know Pedro wouldn't have been there at 13....
If nothing else, the inclusion of K's as a category in your league can act as a tiebreaker. Last year Pujols had 69, Giambi 112 and Sosa 144. I would rank them in the above order even if K's weren't a category, but their inclusion reinforces it.
"You can observe a lot just by watching."