Can you post just a little more information please? When you pick up a player, are they added to your minor league team for this year? There is a ton of talent in the players available, but a lot of them will take time. I'll help you out more when I get a little more information about your rules/roster.
Here are the top pitchers:
Michael Main (I played against him this year
Now that list is based on potential/ability to reach that potential. If you are looking for help this year, the only player that I can imagine being up is Casey Weathers, and another guy that you didn't mention, Joshua Fields. Those two were college closers and could potentially be up this year. Weathers, could actually come up and close with the rumors surrounding Fuentes, but all of that is highly unlikely.
Here are the top hitters:
Nobody on the list could come up this year. According to your needs, I would say LaPorta and Heyward are the best fits for you. They both have huge HR potential. Like I said, just post your roster and I can tell you exactly what I would do