I have been comparing the HP19bii with the HP17bII+ for the last few days at work. Have to say that it was a fair fight - both units are really very good.
HP19bii
Pros:
several lines on the screen allow for clear interpretation of what you are doing and what you need to do
when you need to enter a solver formula, the attached keyboard helps you in doing three or four times faster than the 17bii+
Very good keyboard that never misses a beat.
nicer font (in my opinion) than the other machine
Fantastic menu system.
additional math items: trigonometric, hyperbolic, unit conversion, etc.
When folded is pocketable. No more losing the calculator case!
Graphs (but I have never used them!)
Cons:
Too much real estate taken from your desk
Half of it is not used at all most of the time!
screen contrast is really low. You depend on good lightning conditions.
Problematic battery bay door - unless you have the back door model.
HP17bii+
Pros
Much better form factor.
Elegant silver design.
much better screen contrast - black is black!
Currency exchange on first menu level
Better key feel
Cons
Just one line seen on screen
Good font, but not as nice as the competition above.
Sometimes, I’ve missed some keystrokes. Not often, but it is different from “never”, which was my experience with most other HP calculator.
I hope this helps in selecting the right one for you!