I never liked Yakima for the same reasons.  I don't like the round bars. 
It seems like my mountain bike friends are constantly tightening their 
attachments which seem to slowly turn on the round bars.  I would think 
this would be an even bigger problem if you mounted a Yakima vertically.
Again, I have never owned one so I am obviously biased towards the 
Thule...but there are distinctions that everyone should be aware of.

Chet
Thule Dealer (Just kidding!)