I prefer Boas' temperament over BP's... they are more active and alert... they are a joy to handle.
Boas will generally get bigger, unless you try and acquire a smaller locality(they are quite readily available nowdays).
Nicaragua Boas are hardly much bigger than an adult ball python, and more slender.
Morph-wise, I don't see the BP's advantage... sure, they have more named morphs, but a good share of them look practically the same, are still being worked out, and can possibly be the exact same gene with little difference from each other.
With Boas, well... the hypo gene alone can "generate" animals with colors ranging from red, through orange, to tan, brown, yellow, deep pink... they are incredibly polymorphic.
Breeding though? I have to side with BP's... Boas are a pain to breed. You don't know what's going on throughout... with BP's they either lay within 2 months or so or they don't... with Boas you might end up chewing your fingernails raw waiting until it is absolutely positive that the animal is in fact not going to bring any young. Another point to consider is long-term breeding... if working with morphs is a priority, you end up breeding Boas and getting ALLOT of young... forcing you to either hold back allot of babies of said desired morph, or sell babies you'd rather not under other circumstances.
You also can't work with -that- many pairs per season or you'll drown in babies.
BP's bring allot less young per breeding... allowing you to breed more pairs, thus getting more diversity.
It boils down to preference.