As far as I know, GYSN (str/GYSN) has written a completely new function for generating and replacing key in vBulletin package, which is much more efficient and faster. Also, GYSN code is only obfuscated, not decoded, which improves efficiency as well.
DGT is using the same old system, like SCRiPTMAFiA (R.I.P.).
There is no better or worse. Both work nicely and do the job, so I think this topic is not needed.
Also each Team varies who is out first. Apparently right now Gysn is in the middle of a complete site over haul and have dedicated their time to this. Regardless each put out a quality release and it comes down to who you have come to trust more. As far as keygen's go they both get the job done.