I noticed often times, particular posters will state a conflicting ID and not give any reason behind it - I think it would be educational to give field marks supporting an ID when it conflicts with another's.
I would like to learn, and I'm sure many others would too.
Concerning the ID on this particular bird, my initial impression was Sharp-shinned, based on the "earnest" expression, what I can see from the breast streaking, and the tail feathers (outer feathers longer than inner). Size is tough to judge from photos, but it does appear to be small-ish.
However, this was just my initial reaction, I'm nowhere near an expert on Accipiters.
To the OP, ceasar's link is excellent, here's another link that may help:
http://www.birds.cornell.edu/pfw/AboutBirdsandFeeding/accipiterIDtable.htm