I am also planning on getting a boa. I have a thread over in the boa section you should probably read. Basically research which species stay smaller and buy a baby that you can bring up and learn its temperament and feel comfortable with it before it gets bigger. So far after the research I have done I am leaning toward a Colombian boa.
Link: my rtb thread
edit: Pros: a more outgoing snake that isnt going to stay in its hide all day and able to handle daily. From what I have read they can be as docile as a BP (of course this depends on species and the particular snake).
Cons: they can get big. There are a lot of different boa species that have been bred together making knowing the background of your snake hard to tell and predict. Possibly more bitey.