Raven VII said:
I like the 19" better, of course, but then again they both have the same number of pixels, so ignore me.
This is surely another thing to look at as well. If you're only going to be using one monitor to do all your work on, the bigger the better. As Raven said as well, you might gain 2" in screen size but you will not get any additional pixel resolution.
If you step into a 20", not only do you get an extra 1-3" over a 17 or 19, you also got from a pixel resolution of 1600x1200 up from 1280x1024.
I too work heavily in Adobe programs and know how many menu windows you can have open, so to the less I have to hunt and pick for the tools or artwork, the better.
Now, if your going to use you PB monitor as a dual monitor setup, I'd stay smaller as you could designate one monitor for all your menus and the other for your canvas windows. You'll save a few bucks as well!
I just bought a 20" as it is very hard for me to go home from a 21" to a 15" PB. Plus I wanted all the space I could get to use for my applications. Not to mention watching DVD's!