Don't own either, but I would if it weren't for cost.
The biggest problem with the 70-200VC is the price IMO. If you can get a 70-200Lii refurb for $1699, brand new for @$2100 or even brand new on a sale for $1999, the $1499 price of the Tamron is it's biggest problem. I think that is why it isn't making as many waves as it could. If it was in the $1199 range it would probably be a big hit. Everything I've seen from the lens performance wise really impresses me.
The 24-70VC has a bit more documentation/owner feedback on it because the VC and price give it more of a distinction from Canon's offerings (what the 70-200VC has a problem doing).
If it were me, I would do it (although that 70-200VC price gives me less joy than the 24-70 for what you get). 