If you have sonar X3 (?) and above then you must already have AD2 in some form or other?
Given that, "avant-garde" as a genre can be almost anything then it's surely more about how you use it?
I wouldn't really recommend any of them (AD2, BFD3 or superior) for avant-garde or electronic music as they are primarily for rock, jazz, funk, punk, folk and everything else in the acoustic drum world but they can still be useful, it's a matter of your imagination and how you use it.
As for loading your own samples I'm pretty sure AD2 won't let you, not sure about superior drummer but BFD3 will definitely let you load your own samples. If you were going to spend money on any of the above then I would recommend BFD3 as being the best by some distance.
Also from fxpansion, I would suggest having a look at Tremor for electronic music as well Kamikaze's suggestion of Chromophone.
Steve