If Posey is only having a slow start, I'd easily take him over Nocioni. He's older, but El Chapu has a lot of games under his legs, has been playing through injuries for the last 3 seasons and never rests in the Summer. Plus, last season Posey was an immensely superior defender. Nocioni hustles and is physical, but he doesn't defend.
Alexander is just a terrible player atm. One of the rawest players I've ever seen in the NBA - at the start of last season, he wasn't even able to slide his feet correctly, something most 13 years old can do. There are complains about his work ethic, he's too slow to defend the perimeter, too small to defend inside, a terrible rebounder and not very smart. The only thing he does well is getting separation to get his shot off, but he ends up missing them anyway (doesn't keep balance). In the past Summer League he showed progress attacking the rim from the pinch post with 3 quick dribbles, but the competition was weak. This guy had 4 months of college basketball where he played well above his head and that guaranteed him a high draft pick. Maybe he can some day become a solid bench player, but it's someone you can offer a non-guaranteed contract next season. No point in acquiring him now.