most traditional groups use substation, yes ....

I haven't used XombieSub myself, so I can't say whether it's better or worse overall. SubStation Alpha is kinda dated though ... it was mainly coded for interacting with hardware genlocks and doing tapesubbing. Its UI could also use some work, and it doesn't support much of the newer advanced effect stuff. If XombieSub does, and provides a similar interface, then it'd also be a viable alternative I'd say.