Damn, did you just open one hell of a can of worms...Because there is a hell of a big world beyond Cubase and ProTools.
Cubase hasn't been considered a joke for a while, which is good. It's not a bad program.
A large number of the current DAW systems are very, very good, and have a place amongst serious musicians, mixers and composers.
Digital Performer still ranks supreme for a lot of music producers and film/TV composers (Zimmer, Elfman)...And it can utilize the PT audio system, cards and interfaces. It still has superior MIDI capabilities in some areas and does some nifty things with monophonic pitch detection.
Logic also has a place amongst the serious, though a smaller place.
And speaking of Steinberg, Nuendo is Cubase+everything needed for film, complex surround, specialized file formats etc. Cubase is the low-midgrade Steinberg product: Nuendo is, and always has been the flagship, dating back to its very, very brief days on the Irix platform (no, really).
Now, if we look at the very high end, we have some tools like Merging's Pyramix, Fairlight's impressive stuff, and for hardware, Euphonix, Harrison, Studer (yes, they make digital consoles), and even Otari for broadcast. But I digress.
Of course, the biggie DAW on Linux is Ardour. It supports CoreAudio (OS X) or ALSA/FFADO...No support for Windows users though. But why bother trying to program around Microsoft's inefficiencies? Ardour is very much a serious player. They had a partnership with Solid State Logic for a while, and put out a good package.
Cubase occupies a place in the market that I would describe as prosumer to pro...I wouldn't describe it as one of two 'serious' options. I would describe Cubase as the Honda of the audio production world: It does everything it needs to, but it's no Cadillac, no Rolls, and definitely no Oshkosh truck.