I'm also trying to figure out which bag will function best for work. I'm considering Batignolles Vertical, Cabas Piano, or Saleya MM. I personally don't care for the Large Bucket-if you are short it hits in an odd place-almost hip length.
I have the petit bucket and the cabas piano and I prefer the CP! I am always checking inside the bucket to see if everything is still there as I am worried something might drop out.
The CP bag can hold a lot of stuff, but possibly the large bucket might hold a bit more. The only thing I like about the bucket is the pochette you get with it. I normally place that on top of all my stuff, and that sorta acts as a little barrier with it being attached to the bag via a chain.
Also I think the CP is more comfortable to wear.
Of those two, I prefer the look of a piano. I like the petit bucket though, just the large one is waaaaaaaay big looking imho. I have a bv and it's great if you are interested, a nice updated looking lv that holds quite a bit but when it's not completely filled doesn't sit weird kwim?
Large bucket would hold more than the cabas piano...although cabas piano can hold a reasonable amount of stuff. I don't have either, but I've seen both in real life...the cabas piano is tiny, imho. Large bucket is large, but not overwhelming like some other big bags. I'd say get what fits your needs.