I'm really on the fence about Blue3. And I've read in this forum, as well as the KVR and other forums that most people either prefer GSi's VB3 or Blue3 (with several choosing a couple of other B3 emulators)
VB3 does the job, and as a lot of people have mentioned, they think it comes closest sounding to the real thing more than any other B3 plugin.
I think it comes down to the differences in VB3 and Blue 3 is not that one is better sounding than the other, they just have a different overall sound. Each equally authentic sounding but in slightly different ways. (even though there is that slightly synthy sound in Blue3 on certain presets)
The choice for me would be easy, if I had an extra $100 lying around, I'd add Blue3 to my collection of virtual instruments in a second. But as it is, I'm on a tight budget and I'd have to do some creative financial juggling in order to get Blue3.
I'll probably end up getting it next month or the month after that, but in the meantime, I'm perfectly satisfied with VB3, and even the old Native Instruments B4-II.