We've got a UAD-1, and it's great.

Far as I can see, the difference between the two is that you can get 3rd party plugins for the Powercore - as the API is available to anyone. So, there are more plugins available for the Powercore, but the quality across the board is less tightly regulated.

By and large it seems to just end up with lots of "my DSP is better than your DSP" arguments on user support forums.

But I've never used the TC so I can't comment.

The UAD-1 is the tits though.