I have both EZDrummer and Superior Drummer...
At the risk of sounding silly and obvious, I summarize them this way:
- the former is very easy to setup and use
- the latter is less easy but far superior in capabilities and sound
If I'm in a hurry to get a quick demo going, I might opt more for EZDrummer. But if I want to do a more serious demo then I use Superior Drummer, knowing that I'll spend more time on it.
But when I released my album I went with a real drummer, which had the benefit of sounding the most superior-ist, as well as being easiest to get what I wanted. As much as I fiddled (and enjoyed fiddling with) the Toontrack stuff, nothing beats the real thing for me. But they can sound great and if you spend enough time you can get some pretty exciting sounding drums from Superior Drummer.