I use both and think the BFD way of building kits is far more intuitive than the x drum workflow. For me the Platinum Samples expansions for BFD give BFD the edge.

Both programs though give you a lot of options and flexibility. For the most part personal preference in 1) the workflow and 2) the expansions is what will draw you from one to the other.

I like both Superior Drummer and BFD, with BFD3 Fxpansion have raised the bar, those new kits are astounding. I think BFD has the edge if you want to mix drums from different expansion packs.
 
Superior is still my goto because I have my Sonar templates set up and I know my way around, I am still learning BDF3
 
 

BFD 3 hands down.  They've definitely raised the bar IMHO.
 
SD is good.  BFD 2 and SD were pretty neck and neck.

Addictive is still my "I need this done in a hurry" drum kit.

But BFD 3 is in a class all it's own...

We'll see what SD 3 brings to the table.  They are WAY WAY WAY WAY WAY overdue...

I googled superior drummer 3 back last summer some time and found no info on it at all.
No one even talking about it on the toontrax forums.
You'd have thought someone would know something, like even if it's in beta stage ?
According to Angus_FX BFD3 was three years in development before they started beta testing.
 
I'm in complete agreement as to which is ahead right now.
I'm salivating over their new expansion BFD Imperial drums right now, the demo's sound really nice and my wallet is straining at the leash 
 
Steve

I hear that Steve....

And with all the expansions half off right now...that just makes it worse...

The toontrack guys have been pumping all sorts of stuff out, instead of updating their program.  All these MIDI packs, producer presets and expansion packs. 
I guess they feel comfortable about their main product.  If I had any preferences, it would be a better GUI, expandable screens, and now that I've got the hang of it... I guess it doesn't matter to ME so much...but a little easier work flow with the X drums and mic assignments.  It's not tough, but could be easier for new customers...maybe.
 
Oh yeah... when auditioning individual drums off the Electronic expansion for EZD...which is a HUGE list, no way to scroll.  The window always closes after a selection and you have to reopen.. pick a new... on and on... hard to quickly find what you're looking for.  I mention that because you can import that kit into Superior.