I absolutely love the sloping top tube on my Sherpa.
Its the first bike I've ever owned with a sloping top tube and I was very surprised with how useful it is on a touring bike.
Stopping to talk to other riders or bending down to grab something is easier. Even getting on and off a loaded bike is easier. Handling is not affected. The bars are level with the seat if the bike is designed properly.
I would not buy another touring bike unless it had a sloping top tube now.
I have other touring bikes with horizontal top tubes and I have to admit the new bike has them beat in this regard.