He preferred Vandersteen saying that the Vans were more musical on more recordings more often than Thiels. But he also zeroed in on what Thiel was doing, how we were approaching our work.
On the flip side, Vandersteen's were always been criticized for being dark and slow :-).
He ended up having to defend his design saying that other speakers tend to have the tweeter running a bit too hot at 2-3db more than they should be.