I've got both!
Here's my pro and con list:
BH
Pro: great work bag, lots of LV for the money (big size for its price, meaning), very elegant styling, works in arm crook as well as my shoulder, holds a ton, cell phone pocket plus inside zip pocket. Very lightweight.
Con: open top which for me is a downer in the rain or when things could spill out due to my sometimes weird driving habits. There is a snap hook closure and the bag does stay shut when it's on your shoulder and tucked under your arm, but due to the open top design I wouldn't use it for business travel. it is definitely more 'work related' and not a casual outing type of bag due to its design, IMO but I have taken it shopping a couple times.
Cabas Piano
Pro: great, versatile size, zip top closure, nice structure, cell phone pocket and inside slit pocket, durable lining, looks good on shoulder or in crook of arm, very very versatile everyday bag for errands or work or casual outings. Note: it IS smaller than the BH.
Con: the vachetta bottom is a no-no for some and a vulnerable area for dings and stains; for me I just am careful where I set it down and used a little shining monkey spray to help protect it.
Hope this helps!