I'm not confident yet on Tebow, his sample size is remarkably small. I actually like Hasselback out of that group because he just loves to air it out. Cassel has been picking up steam lately as well, which might actually put him at the top of the list.
This is tough. I keep wanted to believe in Freeman because he's definitely the most talented of the group. I think Hassellbeck is probably the safest option but either Cassel, Freeman or Tebow have the biggest upside.