I don't have the Sonnox and just have an SPL Attacker, but I do have the Logic and various other brands of envelopers (or whatever you want to call them. transient modulators?).
Ok..
I'd rate Logic last as far as sound but seeing the shape you are applying is helpful. I still grab it and insert it sometimes.
Stillwell Audio Transient Monster is next - Can initiate oversampling. Less features but doesn't sound super brittle.
Flux Bittersweet II - You can only adjust the attack but there are also some M/S functions. Considering this is free, I think you should download it. Sounds pretty good.
SPL Attacker - not flexible at all but the sound is there. Also got this one for free. Don't think I would've bought it considering all of my other options are far more flexible.
Voxengo Transgainer - Wow. Love the sound and the most options out of my choices. Would love to put this head to head vs. the Sonnox but considering the price, the choice was pretty easy for me.
Attack and sustain reshaping audio plugin - TransGainer - Voxengo