Like everyone else, if he's there, take alonso. Definitely the highest end bat there.
I've posted this link somewhere before. Not sure if it's here or not. But a friend of mine chatted with Dave Trembley during a ST game this year and he says that Arrieta is gonna be the best of his young arms. That includes Tillman and Matusz. So at this point pass on Arrieta and take Alonso, but if you get room and need an arm, remember Arrieta. He's extremely under-rated.
Here's the link to his article for more info:http://baseballinstinct.com/2009/03/26/ ... -training/