I have two Blacktail TDs and a Wallace Mentor one-piece, all three are nice but there are some definite defining characteristics between them.
The grip is very different with my Mentor being much wider side to side and lower wrist. The Blacktail grip is narrower with a deeper and smaller circumference in the throat. Personal preference on which one you would like, but I prefer the Blacktail grip.
Like someone above said, the limbs on the Blacktail are narrower than the Mentor. Speed is hard to measure without a chronograph, which I don't have. I do know the Blacktail needs a stiffer arrow, which leads to a heavier arrow (same shaft, different spine), and the Blactail seems faster, but both are fast enough.
I feel less vibration in the limbs in the Blacktails than in the Mentor, but that might be the slightly heavier arrows the 'tails are tuned with.
All in all both are great bows. I'd agree that the Blacktail has a slight edge in "refinement", but my Wallace is a really beautiful bow. The Blacktail was also more expensive last time I looked.
You can't really go wrong with either, at least from my experience.