Well, in my opinion, the main differences are thus:
Pro Tools comes with hardware. It won't work without that hardware. If you've already got hardware that's better than an Mbox, maybe you don't need one.
The main difference between Steinberg stuff (Cubase, Nuendo) and Digidesign stuff (Pro Tools)is interface. They work in fundamentally different ways. Which way you use is up to you; it depends on your style.
Interface is important. it's why people still use the MPC60, the Linn 9000, and the SP12. It's because those pieces prioritize making music over sheer volume of features. It's
fun to program a Linn 9000, it's
fun to make beats on an MPC. And fast. And intuitive.
Cubase has many, many windows for all its functions, as does Nuendo. I use Nuendo at home (mainly because of the 32-bit floating-point mix buss - but that's another subject), and as I work, I constantly find myself with 6 or 8 or 11 windows open, none of which relate immediately to what I'm doing, but all of which
could relate, depending on what I'm doing.
I use Pro Tools at the studios where I work, and it's prety straightforward: I've got two main windows. All my mixing and editing information is visible within those two windows. Extra windows over and beyond that are temporary windows.
With two monitors, my Pro Tools session is constantly visible, both mix-wise and tracks-wise.
My Nuendo session is contained in several windows and sub-windows which may or may not make obvious what they're doing to
what, and why.
For me, Pro Tools is by far the better way of working: less cluttered, more direct, more immediately visible. So, for me, it's the better choice. For somebody who likes to think of their production with each part contained in its own container, maybe a Steinberg product would be better. I dunno.
Just seems to me that the interface is the thing, especially when you will use this thing both for personal projects and when you need to get some work done fast for a client.
-Hoax